Technical Round Materials-Computer Science and Engineering-Free Download

1.What is a file?

Answer:
A file is a named location which stores data or information permanently. A file is always stored inside a storage device using file name (e.g. STUDENT.MARKS). A file name normally has primary and secondary name separated by a “.”(DOT).

2.What is a class?

Answer:
A class is a blueprint from which objects are created. A class contains methods and variables associated with an instance of a class.

3.What is an object?

Answer:
An object is an instance of a class. For example
class Abc{ —– This is a class
int a; —— This is a variable
public Abc(); —- This is contractor
public static void main (String args[]) ——- This is a method
{
Abc a= new Abc(); —— This is object creation where ‘a’ is the reference variable or object name
}
}

4.What is a constructor?

Answer:
A constructor is methods which are used to create an Object of class. There are two types of constructor Default & Parameterized constructor.

5.What is the different OOPS principle?

Answer:
The basic OOPS principle are as follows,

• Encapsulation
• Abstraction
• Inheritance
• Polymorphism

6.What is inheritance?

Answer:
Inheritance is property in which the property of a parent class(Superclass) is passed on to child class(Subclass). For example
class Abc{ —– This is a class
int a; —— This is a variable
public void abc(){} — Methods
}
class Xyz extends Abc —–(Extend is the keyword, Xyz is the subclass which inherits the properties of ABC parent class.)
{
public static void main (String args[]) ——- This is a method
{
Abc a= new Abc(); —— This is object creation where ‘a’ is the reference variable or object name
}
}

7.What is polymorphism?

Answer:
Polymorphism is the ability of an object to take on multiple forms. Most commonly polymorphism is used in OOP when a parent class reference is used to refer to a child class object.

8.What are instance and class variables?

Answer:
Instance variable belongs to a particular instance of that class whereas Class variable. A class variable is also known as static variables. For example
public class Abc{
public int a; …….. This is an instance variable
public static int a1;…….. This is a static or class variable
……………………..
……………..
}

9.Compare method and constructor?

Answer:
Constructor: Used to initialize the instance of a class.
Method: Used to perform some function or operation.

Constructor: Doesn’t have a return type.
Method: Has a return type.

10.What is a singleton class?

Answer:
Singleton class limits the number of objects created for a class to one but gives the flexibility of creating more objects if the situation changes.

11.What are the steps for creating the object?

Answer:
An object is first declared then instantiated and at last declared. For example
Abc a= new Abc();

12.What is the different type of access modifiers?

Answer:
There are four type of access modifiers as given below:-
• Visible to the overall package. No modifier needed.
• Private – Visible to class only.
• Public – Visible to the world.
• Protected – Visible to package and subclass.

13.Which is the highest operator precedence in Java

Answer:
The operator with the highest preference is Postfix operators i.e () [].

14.What is an array?

Answer:
The array is a container which holds the fixed number of similar data types.

15.What is the difference between equals() and method and == operator?

Answer:
The equals() is a method and it matches the content of the strings whereas == is an operator and matches object or reference of the strings.

16.Is string class final?

Answer:
Yes

17.What is a wrapper class?

Answer:
To access the primitive data type as an object we use wrapper class. They are following:-

Primitive Type	Wrapper class
boolean	Boolean
char	Character
byte	Byte
short	Short
int	Integer
long	Long
float	Float
double	Double

18.Difference between overloading and overriding?

Answer:
Overloading is when two or more methods in the same class have the same method name but different parameters(i.e different method signatures).
Overriding is when two methods having the same method name and parameters (i.e., method signature) but one of the methods is in the parent class and the other is in the child class.

19.What are multiple inheritances in Java?

Answer:
Java supports multiple inheritances i.e the ability of a class to implement more than one interface. A class can implement multiple Interfaces but cannot extends multiple classes.

20.What is a stream?

Answer:
A stream can be defined as the sequence of data. There is two type of streams.
InputStream: Used to read a data from a source.
OutPut Stream: Used to write a data into a destination.

21.What is a Character stream?

Answer:
Java Character stream is basically used to perform input and output for 16 bit Unicode. The main classes users are FileReader and FileWriter which internally uses FileInputStream and FileOutputStream so the basic difference is that FileReader and FileWriter read and writes two bites at a time respectively.

22.What is a Byte stream?

Answer:
Java Byte stream is basically used to perform input and output for 8 bit Unicode.
The main classes related to byte streams are FileInputStream and FileOutputStream.

23.What is an Interface?

Answer:
The interface is a reference type in Java, similar to the class but its collection of abstract methods. A class can implement multiple interfaces.

24.Difference between class and interface?

Answer:
Below are the difference between Interface and class:-

• The interface cannot be instantiated.
• An interface doesn’t have any constructors.
• Interface only have abstract methods.
• A class implements an interface and extends a class.
• An interface can extend multiple interfaces.

25.What is an abstract class?

Answer:
A class which contains the abstract keyword in a declaration is called abstract class. The properties of the abstract class are as follows:-

• Abstract classes may or may not contain abstract methods but, if a class has at least one abstract method, then it must be declared abstract.
• The abstract class cannot be instantiated.
• To use an abstract class, we have to inherit it from another class.
• If we inherit an abstract class, then we have to provide implementations to all the abstract methods in it.

? Question 1. What Is An Object In C++?

Answer :

An object is a package that contains related data and instructions. The data relates to what the object represents, while the instructions define how this object relates to other objects and itself.

? Question 2. What Is A Message?

Answer :

A message is a signal from one object to another requesting that a computation take place. It is roughly equivalent to a function call in other languages.

? Question 3. What Is A Class?

Answer :

A class defines the characteristics of a certain type of object. It defines what its members will remember, the messages to which they will respond, and what form the response will take.

? Question 4. What Is An Instance?

Answer :

An individual object that is a member of some class.

? Question 5. What Is A Super-class?

Answer :

Given a class, a super-class is the basis of the class under consideration. The given class is defined as a subset (in some respects) of the super-class. Objects of the given class potentially posses all the characteristics belonging to objects of the super-class.

? Question 6. What Is Inheritance?

Answer :

Inheritance is property such that a parent (or super) class passes the characteristics of itself to children (or sub) classes that are derived from it. The sub-class has the option of modifying these characteristics in order to make a different but fundamentally related class from the super-class.

? Question 7. To What Does Message Protocol Refer?

Answer :

An object’s message protocol is the exact form of the set of messages to which the object can respond.

? Question 8. What Is Polymorphism?

Answer :

Polymorphism refers to the ability of an object to respond in a logically identical fashion to messages of the same protocol, containing differing types of objects. Consider 1 + 5 and 1 + 5.1. In the former, the message “+ 5” is sent to an object of class integer (1). In the later, the message “+ 5.1” is sent to the same integer object. The form of the message (its protocol) is identical in both cases. What differs is the type of object on the right-hand side of these messages. The former is an integer object (5) while the later is a floating point object (5.1). The receiver (1) appears (to other objects) to respond in the same way to both messages. Internally, however, it knows that it must treat the two types of objects differently in order to obtain the same overall response.

? Question 9. What Are Instance Variables?

Answer :

These represent an object’s private memory. They are defined in an object’s class.

? Question 10. What Are Class Variables?

Answer :

These represent a class’s memory which it shares with each of its instances.

? Question 11. What Is A Method?

Answer :

A method is a class’s procedural response to a given message protocol. It is like the definition of a procedure in other languages.

? Question 12. In C++ What Is A Constructor? A Destructor?

Answer :

A constructors and destructors are methods defined in a class that are invoked automatically when an object is created or destroyed. They are used to initialize a newly allocated object and to cleanup behind an object about to be removed.

? Question 13. Compare And Contrast C And C++.?

Answer :

Comparison: C++ is an extension to the C language. When C++ is used as a procedural language, there are only minor syntactical differences between them.

Contrast: When used as a procedural language, C++ is a better C because:

• It vigorously enforces data typing conventions.
• It allows variables to be defined where they are used.
• It allows the definition of real (semantically significant) constants.
• It allows for automatic pointer dereferencing.
• It supports call-by-reference in addition to call-by-value in functions.
• It supports tentative variable declarations (when the type and location of a variable cannot be known before hand.

As an object oriented language, C++ introduces much of the OOP paradigm while allowing a mixture of OOP and procedural styles.

? Question 14. What Is Operator Overloading?

Answer :

It is the process of, and ability to redefine the way an object responds to a C++ operator symbol. This would be done in the object’s class definition.

? Question 15. What Is Cin And Cout?

Answer :

They are objects corresponding to a program’s default input and output files.

Contrast procedural and object oriented programming.

The procedural paradigm performs computation through a step-by-step manipulation of data items. Solving problems this way is akin to writing a recipe. ie: All the ingredients (data items) are defined. Next a series of enumerated steps (statements) are defined to transform the raw ingredients into a finished meal.

The object oriented model, in contrast, combines related data and procedural information into a single package called an object. Objects are meant to represent logically separate entities (like real world objects). Objects are grouped together (and defined by) classes. (This is analogous to user defined data types in procedural languages.) Classes may pass-on their “makeup” to classes derived from them. In this way, Objects that are of a similar yet different nature need not be defined from scratch.

Computation occurs though the intercommunication of objects. Programming this way is like writing a play. First the characters are defined with their attributes and personalities. Next the dialog is written so that the personalities interact. The sum total constitutes a drama.

? Question 16. How Do You Link A C++ Program To C Functions?

Answer :

By using the extern “C” linkage specification around the C function declarations.

You should know about mangled function names and type-safe linkages. Then you should explain how the extern “C” linkage specification statement turns that feature off during compilation so that the linker properly links function calls to C functions.

? Question 17. Explain The Scope Resolution Operator.?

Answer :

The scope resolution operator permits a program to reference an identifier in the global scope that has been hidden by another identifier with the same name in the local scope.

The answer can get complicated. It should start with “colon-colon,” however. (Some readers had not heard the term, “scope resolution operator,” but they knew what :: means. You should know the formal names of such things so that you can understand all communication about them.) If you claim to be well into the design or use of classes that employ inheritance, you tend to address overriding virtual function overrides to explicitly call a function higher in the hierarchy. That’s good knowledge to demonstrate, but address your comments specifically to global scope resolution. Describe C++’s ability to override the particular C behavior where identifiers in the global scope are always hidden by similar identifiers in a local scope.

? Question 18. What Are The Differences Between A C++ Struct And C++ Class?

Answer :

The default member and base class access specifiers are different.

This is one of the commonly misunderstood aspects of C++. Believe it or not, many programmers think that a C++ struct is just like a C struct, while a C++ class has inheritance, access specifiers, member functions, overloaded operators, and so on. Some of them have even written books about C++. Actually, the C++ struct has all the features of the class.

The only differences are that a struct defaults to public member access and public base class inheritance, and a class defaults to the private access specifier and private base class inheritance. Getting this question wrong does not necessarily disqualify you because you will be in plenty of good company. Getting it right is a definite plus.

? Question 19. How Many Ways Are There To Initialize An Int With A Constant?

Answer :

There are two formats for initializers in C++ as shown in Example 1. Example 1(a) uses the traditional C notation, while Example 1(b) uses constructor notation. Many programmers do not know about the notation in Example 1(b), although they should certainly know about the first one. Many old-timer C programmers who made the switch to C++ never use the second idiom, although some wise heads of C++ profess to prefer it.

A reader wrote to tell me of two other ways, as shown in Examples 2(a) and 2(b), which made me think that maybe the answer could be extended even further to include the initialization of an int function parameter with a constant argument from the caller.

? Question 20. How Does Throwing And Catching Exceptions Differ From Using Setjmp And Longjmp?

Answer :

The throw operation calls the destructors for automatic objects instantiated since entry to the try block.

Exceptions are in the mainstream of C++ now, so most programmers, if they are familiar with setjmp and longjmp, should know the difference. Both idioms return a program from the nested depths of multiple function calls to a defined position higher in the program.

The program stack is “unwound” so that the state of the program with respect to function calls and pushed arguments is restored as if the calls had not been made. C++ exception handling adds to that behavior the orderly calls to the destructors of automatic objects that were instantiated as the program proceeded from within the try block toward where the throw expression is evaluated.

It’s okay to discuss the notational differences between the two idioms. Explain the syntax of try blocks, catch exception handlers, and throw expressions. Then specifically address what happens in a throw that does not happen in a longjmp. Your answer should reflect an understanding of the behavior described in the answer just given.

One valid reason for not knowing about exception handling is that your experience is exclusively with older C++ compilers that do not implement exception handling. I would prefer that you have at least heard of exception handling, though.

It is not unusual for C and C++ programmers to be unfamiliar with setjmp/ longjmp. Those constructs are not particularly intuitive. A C programmer who has written recursive descent parsing algorithms will certainly be familiar with setjmp/ longjmp.

Others might not, and that’s acceptable. In that case, you won’t be able to discuss how setjmp/longjmp differs from C++ exception handling, but let the interview turn into a discussion of C++ exception handling in general. That conversation will reveal to the interviewer a lot about your overall understanding of C++.

? Question 21. What Is Your Reaction To This Line Of Code?

Answer :

delete this;

It’s not a good practice.

A good programmer will insist that the statement is never to be used if the class is to be used by other programmers and instantiated as static, extern, or automatic objects. That much should be obvious.

The code has two built-in pitfalls. First, if it executes in a member function for an extern, static, or automatic object, the program will probably crash as soon as the delete statement executes. There is no portable way for an object to tell that it was instantiated on the heap, so the class cannot assert that its object is properly instantiated.

Second, when an object commits suicide this way, the using program might not know about its demise. As far as the instantiating program is concerned, the object remains in scope and continues to exist even though the object did itself in. Subsequent dereferencing of the pointer can and usually does lead to disaster.

A reader pointed out that a class can ensure that its objects are instantiated on the heap by making its destructor private. This idiom necessitates a kludgy DeleteMe kind of function because the instantiator cannot call the delete operator for objects of the class. The DeleteMe function would then use “delete this.”

I got a lot of mail about this issue. Many programmers believe that delete this is a valid construct. In my experience, classes that use delete this when objects are instantiated by users usually spawn bugs related to the idiom, most often when a program dereferences a pointer to an object that has already deleted itself.

? Question 22. What Is A Default Constructor?

Answer :

A constructor that has no arguments or one where all the arguments have default argument values.

If you don’t code a default constructor, the compiler provides one if there are no other constructors. If you are going to instantiate an array of objects of the class, the class must have a default constructor.

? Question 23. What Is A Conversion Constructor?

Answer :

A constructor that accepts one argument of a different type.

The compiler uses this idiom as one way to infer conversion rules for a class. A constructor with more than one argument and with default argument values can be interpreted by the compiler as a conversion constructor when the compiler is looking for an object of the type and sees an object of the type of the constructor’s first argument.

? Question 24. What Is The Difference Between A Copy Constructor And An Overloaded Assignment Operator?

Answer :

A copy constructor constructs a new object by using the content of the argument object. An overloaded assignment operator assigns the contents of an existing object to another existing object of the same class.

First, you must know that a copy constructor is one that has only one argument, which is a reference to the same type as the constructor. The compiler invokes a copy constructor wherever it needs to make a copy of the object, for example to pass an argument by value. If you do not provide a copy constructor, the compiler creates a member-by-member copy constructor for you.

You can write overloaded assignment operators that take arguments of other classes, but that behavior is usually implemented with implicit conversion constructors. If you do not provide an overloaded assignment operator for the class, the compiler creates a default member-by-member assignment operator.

This discussion is a good place to get into why classes need copy constructors and overloaded assignment operators. By discussing the requirements with respect to data member pointers that point to dynamically allocated resources, you demonstrate a good grasp of the problem.

? Question 25. When Should You Use Multiple Inheritance?

Answer :

There are three acceptable answers: “Never,” “Rarely,” and “When the problem domain cannot be accurately modeled any other way.”

There are some famous C++ pundits and luminaries who disagree with that third answer, so be careful.

Let’s digress to consider this issue lest your interview turn into a religious debate. Consider an Asset class, Building class, Vehicle class, and CompanyCar class. All company cars are vehicles. Some company cars are assets because the organizations own them. Others might be leased. Not all assets are vehicles. Money accounts are assets. Real-estate holdings are assets. Some real-estate holdings are buildings. Not all buildings are assets. Ad infinitum.

When you diagram these relationships, it becomes apparent that multiple inheritance is an intuitive way to model this common problem domain. You should understand, however, that multiple inheritance, like a chainsaw, is a useful tool that has its perils, needs respect, and is best avoided except when nothing else will do. Stress this understanding because your interviewer might share the common bias against multiple inheritance that many object-oriented designers hold.

? Question 26. What Is A Virtual Destructor?

Answer :

The simple answer is that a virtual destructor is one that is declared with the virtual attribute.

The behavior of a virtual destructor is what is important. If you destroy an object through a pointer or reference to a base class, and the base-class destructor is not virtual, the derived-class destructors are not executed, and the destruction might not be complete.

? Question 27. Explain The Isa And Hasa Class Relationships. How Would You Implement Each In A Class Design?

Answer :

A specialized class “is a” specialization of another class and, therefore, has the ISA relationship with the other class. An Employee ISA Person. This relationship is best implemented with inheritance. Employee is derived from Person.

A class may have an instance of another class. For example, an Employee “has a” Salary, therefore the Employee class has the HASA relationship with the Salary class. This relationship is best implemented by embedding an object of the Salary class in the Employee class.

The answer to this question reveals whether you have an understanding of the fundamentals of object-oriented design, which is important to reliable class design.

There are other relationships. The USESA relationship is when one class uses the services of another. The Employee class uses an object (cout) of the ostream class to display the employee’s name onscreen, for example. But if you get ISA and HASA right, you usually don’t need to go any further.

? Question 28. When Is A Template A Better Solution Than A Base Class?

Answer :

When you are designing a generic class to contain or otherwise manage objects of other types, when the format and behavior of those other types are unimportant to their containment or management, and particularly when those other types are unknown (thus the genericity) to the designer of the container or manager class.

Prior to templates, you had to use inheritance; your design might include a generic List container class and an application-specific Employee class. To put employees in a list, a ListedEmployee class is multiply derived (contrived) from the Employee and List classes. These solutions were unwieldy and error-prone. Templates solved that problem.

? Question 29. What Is The Difference Between C And C++ ? Would You Prefer To Use One Over The Other ?

Answer :

C is based on structured programming whereas C++ supports the object-oriented programming paradigm.Due to the advantages inherent in object-oriented programs such as modularity and reuse, C++ is preferred. However almost anything that can be built using C++ can also be built using C.

? Question 30. What Are The Access Privileges In C++ ? What Is The Default Access Level ?

Answer :

The access privileges in C++ are private, public and protected. The default access level assigned to members of a class is private. Private members of a class are accessible only within the class and by friends of the class. Protected members are accessible by the class itself and it’s sub-classes. Public members of a class can be accessed by anyone.

? Question 31. What Is Data Encapsulation ?

Answer :

Data Encapsulation is also known as data hiding. The most important advantage of encapsulation is that it lets the programmer create an object and then provide an interface to the object that other objects can use to call the methods provided by the object.

The programmer can change the internal workings of an object but this transparent to other interfacing programs as long as the interface remains unchanged.

? Question 32. What Is Inheritance ?

Answer :

Inheritance is the process of deriving classes from other classes. In such a case, the sub-class has an ‘is-a’ relationship with the super class. For e.g. vehicle can be a super-class and car can be a sub-class derived from vehicle. In this case a car is a vehicle.

The super class ‘is not a’ sub-class as the sub- class is more specialized and may contain additional members as compared to the super class. The greatest advantage of inheritance is that it promotes generic design and code reuse.

? Question 33. What Is Multiple Inheritance ? What Are It’s Advantages And Disadvantages ?

Answer :

Multiple Inheritance is the process whereby a sub-class can be derived from more than one super class. The advantage of multiple inheritance is that it allows a class to inherit the functionality of more than one base class thus allowing for modeling of complex relationships.

The disadvantage of multiple inheritance is that it can lead to a lot of confusion when two base classes implement a method with the same name.

? Question 34. What Do The Keyword Static And Const Signify?

Answer :

When a class member is declared to be of a static type, it means that the member is not an instance variable but a class variable. Such a member is accessed using Classname.Membername (as opposed to Object.Membername). Const is a keyword used in C++ to specify that an object’s value cannot be changed.

? Question 35. How Is Memory Allocated/deallocated In C ? How About C++ ?

Answer :

Memory is allocated in C using malloc() and freed using free(). In C++ the new() operator is used to allocate memory to an object and the delete() operator is used to free the memory taken up by an object.

? Question 36. What Is Uml?

Answer :

UML refers to Unified Modeling Language. It is a language used to model OO problem spaces and solutions.

? Question 37. What Is The Difference Between A Shallow Copy And A Deep Copy?

Answer :

A shallow copy simply creates a new object and inserts in it references to the members of the original object. A deep copy constructs a new object and then creates in it copies of each of the members of the original object.

1)Who invented C Language?
Dennis Ritchie in 1972 developed a new language by inheriting the features of both BCPL and B and adding additional features. He named the language as just C.

2) Who invented B Language?
Ken Thomson at AT&T Bell Labs developed a language and named it B. Even the B language was found to have some short comings to support development of both business applications and system software.

3) Who invented BCPL Language?
Basic Combined Programming Language(BCPL) was developed by Martin Richards, Cambridge university.

4) Why C Language?
C is one of the high level languages. It is a general purpose language, which means it can be used to write programs of any sort.

5) What are the features of C Langauges?

1. In C one can write programs like that of high level languages as in COBOL, BASIC, FORTRAN etc. as well as it permits very close interaction with the inner workings of the computer.

2. It is a general purpose programming language. It is usually called system programming language but equally suited to writing a variety of applications.

3. It supports various data types.

4. It follows the programming style based on fundamental control flow constructions for structured programming.

5. Functions may be pre–defined or user defined and they may return values of basic types, structures, unions or pointers.

6)What are the advantages of c language?

• Easy to write
• Rich set of operators and functions that are built–in
• Support for bit–wise operation
• Flexible use of pointers
• Direct control over the hardware
• Ability to access BIOS/DOS routines
• Interacting using Interrupts
• Ability to write TSR programs
• Ability to create .COM files
• Ability to create library files (.LIB)
• Ability to write interface programs
• Incorporating assembly language in C program

7) What are the disadvantages of c langauge?

• C is considered difficult to learn
• Because of its conciseness, the code can be difficult to follow
• It is not suited to applications that require a lot of report formatting and data file manipulation.

8) What are the salient features of c languages?

1. The following are the salient features of C language are :

2. C is called a middle level language

3. C supports structured design approach

4. C is extensible

5. C is rich in data types and operators

6. C is portable

9) What is a header file?
Header files provide the definitions and declarations for the library functions. Thus, each header file contains the library functions along with the necessary definitions and declarations. For example, stdio.h, math.h, stdlib.h, string.h etc.

10) What is character set?
Character set is the set of characters allowed and supported in the programming language. Generally a program is a collection of instructions, which contain groups of characters. Only a limited set of characters is allowed to write instructions in the program.

11) What is C token?
The smallest individual units of a C program are known as tokens.

12) List the different types of C tokens?

• Constants
• Identifiers
• Keywords
• Operators
• Special symbols
• Strings

13) What is a string?
A string is a sequence of characters ending with NUL. It can be treated as a one–dimensional array of characters terminated by a NUL character.

14) What are qualifiers?
Qualifiers or modifiers are identifiers that may precede the scalar data types (except float) to specify the number of bits used for representing the respective type of data in memory. The qualifiers in C are short, long, signed, and unsigned.

15) What is a function?
A function is a set of statements to perform a specific task.

16) What is a constant?
A constant is a value that does not change during the program execution. A constant used in C does not occupy memory.

17) What are the different types of constants?
There are five types of constants. They are :

1. Integer constants

2. Floating point constants

3. Character constants

4. String literals

5. Enumeration constants

18) What is variable?
An identifier is used to identify and store some value. If the value of the identifier is changed during the execution of the program, then the identifier is known as variable.

19) What are the rules for the identifier?

• The first character must be an alphabet or underscore (_)
• Digits may be included in the variable
• The maximum number of characters in a word are 32 (It may vary depending upon the platform)
• No other special characters are allowed.

20) What are global variables?
Global Variables are those, which are required to be acccessed by all the functions defined after their declaration. So, the variables declared before the main {) can be acccessed by all the functions, which follow their declaration.

21) What is a keyword?
Keywords are those words of C which have predefined meaning assigned by the C language. They form a part of the database required by the C compiler.

22) What are the different types of c instructions?
There are basically three types of instructions in C are :

1. Type Declaration Instruction

2. Arithmetic Instruction

3. Control Instruction

23) What is an expression?
Expression is defined as a combination of operands and operators to obtain some computation. Operands represent variables or values and The operator tells is what operation to be performed.

24) What are the types of data files?
There are two types of data files :

• stream oriented or standard data files
• system oriented or low level data files

25) Why C is called a middle level language?
C combines the features of both Assembly Level Languages (Low Level Languages) and Higher Level Languages. For this reason, C is referred to as a Middle Level Language. The feature of ALLs is that of enabling us to develop system level programs and the features of HLLs are those of higher degree of readability and machine independence.

26) How can variables be characterized?
The variables can be categorized by storage class as well as by data type. The storage class specifies the portion of the program within which the variables are recognized.

27) Give the rules for variable declaration?
The rules for variable declaration in C are given below :

• A variable name consists of alphabets, digits and the underscore (_) character
• The length of variable should be kept upto 8 characters though your system may allow upto 40 characters
• They must begin with an alphabet
• Some systems also recognize an underscore as the first character
• White space and commas are not allowed
• Any reserved word (keyword) cannot be used as a variable name.

28) What is the purpose of type declarations?
The type declaration allow to create a synonym for other data types. Its syntax is type def type identifier; The declaration type def unsigned long int INTEGER

29) What is recursion?
C language a function may call another function. When a function calls itself, it is referred to as recursive call and the process is known as recursion. C provides very good facilities for recursion.

30) What is data types?
Data types refer to the classes of data that can be manipulated by C programs. The three fundamental data types supported by C are character, integer and real type.

1. What is data structure?
The logical and mathematical model of a particular organization of data is called data structure. There are two types of data structure
1.Linear
2.Nonlinear

2. What are the goals of Data Structure?
It must rich enough in structure to reflect the actual relationship of data in real world.
The structure should be simple enough for efficient processing of data.

3. What does abstract Data Type Mean?
Data type is a collection of values and a set of operations on these values. Abstract data type refer to the mathematical concept that define the data type.It is a useful tool for specifying the logical properties of a data type.ADT consists of two parts
1.Values definition
2.Operation definition

4. What is the difference between a Stack and an Array?

1. Stack is a ordered collection of items

2. Stack is a dynamic object whose size is constantly changing as items are pushed and popped .

3. Stack may contain different data types

4. Stack is declared as a structure containing an array to hold the element of the stack, and an integer to indicate the current stack top within the array.

ARRAY

• Array is an ordered collection of items
• Array is a static object i.e. no of item is fixed and is assigned by the declaration of the array
• It contains same data types.
• Array can be home of a stack i.e. array can be declared large enough for maximum size of the stack.

5. What do you mean by recursive definition?
The definition which defines an object in terms of simpler cases of itself is called recursive definition.

6. What is sequential search?
In sequential search each item in the array is compared with the item being searched until a match occurs. It is applicable to a table organized either as an array or as a linked list.

7. What actions are performed when a function is called?
When a function is called
i) arguments are passed
ii) local variables are allocated and initialized
ii) transferring control to the function

8. What actions are performed when a function returns?
i) Return address is retrieved
ii) Function’s data area is freed
iii) Branch is taken to the return address

9. What is a linked list?
A linked list is a linear collection of data elements, called nodes, where the linear order is given by pointers. Each node has two parts first part contain the information of the element second part contains the address of the next node in the list.

10. What are the advantages of linked list over array (static data structure)?
The disadvantages of array are

1. unlike linked list it is expensive to insert and delete elements in the array

2. One can’t double or triple the size of array as it occupies block of memory space.

In linked list

1. each element in list contains a field, called a link or pointer which contains the address of the next element

2. Successive element’s need not occupy adjacent space in memory.

11. Can we apply binary search algorithm to a sorted linked list, why?
No we cannot apply binary search algorithm to a sorted linked list, since there is no way of indexing the middle element in the list. This is the drawback in using linked list as a data structure.

12. What do you mean by free pool?
Pool is a list consisting of unused memory cells which has its own pointer.

13. What do you mean by garbage collection?
It is a technique in which the operating system periodically collects all the deleted space onto the free storage list.It takes place when there is minimum amount of space left in storage list or when "CPU" is ideal.The alternate method to this is to immediately reinsert the space into free storage list which is time consuming.

14. What do you mean by overflow and underflow? 1

• When new data is to be inserted into the data structure but there is no available space i.e. free storage list is empty this situation is called overflow.
• When we want to delete data from a data structure that is empty this situation is called underflow.

15. What are the disadvantages array implementations of linked list?
1.The no of nodes needed can’t be predicted when the program is written.
2.The no of nodes declared must remain allocated throughout its execution

16. What is a queue? 1
A queue is an ordered collection of items from which items may be deleted at one end (front end) and items inserted at the other end (rear end).It obeys FIFO rule there is no limit to the number of elements a queue contains.

17. What is a priority queue?
The priority queue is a data structure in which the intrinsic ordering of the elements (numeric or alphabetic)
Determines the result of its basic operation. It is of two types
i) Ascending priority queue- Here smallest item can be removed (insertion is arbitrary)
ii) Descending priority queue- Here largest item can be removed (insertion is arbitrary)

18. What are the disadvantages of sequential storage?
1.Fixed amount of storage remains allocated to the data structure even if it contains less element.
2.No more than fixed amount of storage is allocated causing overflow

19. What are the disadvantages of representing a stack or queue by a linked list?
i) A node in a linked list (info and next field) occupies more storage than a corresponding element in an array.
ii) Additional time spent in managing the available list.

20. What is dangling pointer and how to avoid it?

• After a call to free(p) makes a subsequent reference to *p illegal, i.e. though the storage to p is freed but the value of p(address) remain unchanged .so the object at that address may be used as the value of *p (i.e. there is no way to detect the illegality).Here p is called dangling pointer.
• To avoid this it is better to set p to NULL after executing free(p).The null pointer value doesn’t reference a storage location it is a pointer that doesn’t point to anything.

21. What are the disadvantages of linear list?
i) We cannot reach any of the nodes that precede node (p)
ii) If a list is traversed, the external pointer to the list must be persevered in order to reference the list again

22. Define circular list?
In linear list the next field of the last node contain a null pointer, when a next field in the last node contain a pointer back to the first node it is called circular list.
Advantages – From any point in the list it is possible to reach at any other point

23. What are the disadvantages of circular list?
i) We can’t traverse the list backward
ii) If a pointer to a node is given we cannot delete the node

24. Define double linked list?
It is a collection of data elements called nodes, where each node is divided into three parts
i) An info field that contains the information stored in the node
ii) Left field that contain pointer to node on left side
iii) Right field that contain pointer to node on right side

25. Is it necessary to sort a file before searching a particular item ?
If less work is involved in searching a element than to sort and then extract, then we don’t go for sort
If frequent use of the file is required for the purpose of retrieving specific element, it is more efficient to sort the file.Thus it depends on situation.

26. What are the issues that hamper the efficiency in sorting a file?
The issues are
i) Length of time required by the programmer in coding a particular sorting program
ii) Amount of machine time necessary for running the particular program
iii)The amount of space necessary for the particular program .

27. Calculate the efficiency of sequential search?
The number of comparisons depends on where the record with the argument key appears in the table

1. If it appears at first position then one comparison

2. If it appears at last position then n comparisons

3. Average=(n+1)/2 comparisons

4. Unsuccessful search n comparisons

5. Number of comparisons in any case is O (n).

28. Is any implicit arguments are passed to a function when it is called?
Yes there is a set of implicit arguments that contain information necessary for the function to execute and return correctly. One of them is return address which is stored within the function’s data area, at the time of returning to calling program the address is retrieved and the function branches to that location.

29. Parenthesis is never required in Postfix or Prefix expressions, why?
Parenthesis is not required because the order of the operators in the postfix /prefix expressions determines the actual order of operations in evaluating the expression

30. List out the areas in which data structures are applied extensively?

1. Compiler Design,

2. Operating System,

3. Database Management System,

4. Statistical analysis package,

5. Numerical Analysis,

6. Graphics,

7. Artificial Intelligence,

8. Simulation

31. What are the major data structures used in the following areas : network data model & Hierarchical data model?
RDBMS – Array (i.e. Array of structures)
Network data model – Graph
Hierarchical data model – Trees

32. If you are using C language to implement the heterogeneous linked list, what pointer type will you use?
The heterogeneous linked list contains different data types in its nodes and we need a link, pointer to connect them. It is not possible to use ordinary pointers for this. So we go for void pointer. Void pointer is capable of storing pointer to any type as it is a generic pointer type.

33. Minimum number of queues needed to implement the priority queue?
Two. One queue is used for actual storing of data and another for storing priorities.

34. What is the data structures used to perform recursion?

• Stack. Because of its LIFO (Last In First Out) property it remembers its ‘caller’ so knows whom to return when the function has to return. Recursion makes use of system stack for storing the return addresses of the function calls.
• Every recursive function has its equivalent iterative (non-recursive) function. Even when such equivalent iterative procedures are written, explicit stack is to be used.

35. What are the notations used in Evaluation of Arithmetic Expressions using prefix and postfix forms?
Polish and Reverse Polish notations.

36. Convert the expression ((A + B) * C – (D – E) ^ (F + G)) to equivalent Prefix and Postfix notations?
1.Prefix Notation:
^ – * +ABC – DE + FG
2.Postfix Notation:
AB + C * DE – – FG + ^

37. Sorting is not possible by using which of the following methods?
(a) Insertion
(b) Selection
(c) Exchange
(d) Deletion
(d) Deletion.
Using insertion we can perform insertion sort, using selection we can perform selection sort, using exchange we can perform the bubble sort (and other similar sorting methods). But no sorting method can be done just using deletion.

38. List out few of the Application of tree data-structure?

1. The manipulation of Arithmetic expression,

2. Symbol Table construction,

3. Syntax analysis.

39. List out few of the applications that make use of Multilinked Structures?
Sparse matrix, Index generation.

40. in tree construction which is the suitable efficient data structure?
(A) Array (b) Linked list (c) Stack (d) Queue (e) none
(b) Linked list

41. What is the type of the algorithm used in solving the 8 Queens problem?
Backtracking

42. In an AVL tree, at what condition the balancing is to be done?
If the ‘pivotal value’ (or the ‘Height factor’) is greater than 1 or less than –1.

43. In RDBMS, what is the efficient data structure used in the internal storage representation?
B+ tree. Because in B+ tree, all the data is stored only in leaf nodes, that makes searching easier. This corresponds to the records that shall be stored in leaf nodes.

45. One of the following tree structures, which is, efficient considering space and time complexities?
a) Incomplete Binary Tree.
b) Complete Binary Tree.
c) Full Binary Tree.
b) Complete Binary Tree.
By the method of elimination:
Full binary tree loses its nature when operations of insertions and deletions are done. For incomplete binary trees,
extra property of complete binary tree is maintained even after operations like additions and deletions are done on it.

46. What is a spanning Tree?
A spanning tree is a tree associated with a network. All the nodes of the graph appear on the tree once. A minimum spanning tree is a spanning tree organized so that the total edge weight between nodes is minimized.

47. Does the minimum spanning tree of a graph give the shortest distance between any 2 specified nodes?
No.Minimal spanning tree assures that the total weight of the tree is kept at its minimum. But it doesn’t mean that the distance between any two nodes involved in the minimum-spanning tree is minimum.

48. Whether Linked List is linear or Non-linear data structure?
According to Storage Linked List is a Non-linear one.

1.What is JVM?

The Java interpreter along with the run time environment required to run the Java application in called as Java virtual machine(JVM)

2. What is the most important feature of Java?

Java is a platform independent language.

3. What do you mean by platform independence?

Platform independence means that we can write and compile the java code in one platform (eg Windows) and can execute the class in any other supported platform eg (Linux,Solaris,etc).

4. What is the difference between a JDK and a JVM?

JDK is Java Development Kit which is for development purpose and it includes execution environment also. But JVM is purely a run time environment and hence you will not be able to compile your source files using a JVM.

5. What is the base class of all classes?

java.lang.Object

6. What are the access modifiers in Java?

There are 3 access modifiers. Public, protected and private, and the default one if no identifier is specified is called friendly, but programmer cannot specify the friendly identifier explicitly.

7. What is are packages?

A package is a collection of related classes and interfaces providing access protection and namespace management.

8. What is meant by Inheritance and what are its advantages?

Inheritance is the process of inheriting all the features from a class. The advantages of inheritance are reusability of code and accessibility of variables and methods of the super class by sub classes.

9. What is the difference between superclass and subclass?

A super class is a class that is inherited whereas sub class is a class that does the inheriting.

10. What is an abstract class?

An abstract class is a class designed with implementation gaps for sub classes to fill in and is deliberately incomplete.

11. What are the states associated in the thread?

Thread contains ready, running, waiting and dead states.

12. What is synchronization?

Synchronization is the mechanism that ensures that only one thread is accessed the resources at a time.

13. What is deadlock?

When two threads are waiting each other and can’t precede the program is said to be deadlock.

14. What is an applet?

Applet is a dynamic and interactive program that runs inside a web page displayed by a java capable browser

15. What is the lifecycle of an applet?

• init() method - Can be called when an applet is first loaded
• start() method - Can be called each time an applet is started.
• paint() method - Can be called when the applet is minimized or maximized.
• stop() method - Can be used when the browser moves off the applet’s page.
• destroy() method - Can be called when the browser is finished with the applet.

16. How do you set security in applets?

using setSecurity Manager() method

17. What is a layout manager and what are different types of layout managers available in java AWT?

A layout manager is an object that is used to organize components in a container. The different layouts are available are FlowLayout, BorderLayout, CardLayout, GridLayout and GridBagLayout

18. What is JDBC?

JDBC is a set of Java API for executing SQL statements. This API consists of a set of classes and interfaces to enable programs to write pure Java Database applications.

19. What are drivers available?

a) JDBC-ODBC Bridge driver b) Native API Partly-Java driver

c) JDBC-Net Pure Java driver d) Native-Protocol Pure Java driver

20. What is stored procedure?

Stored procedure is a group of SQL statements that forms a logical unit and performs a particular task. Stored Procedures are used to encapsulate a set of operations or queries to execute on database. Stored procedures can be compiled and executed with different parameters and results and may have any combination of input/output parameters.

21. What is the Java API?

The Java API is a large collection of ready-made software components that provide many useful capabilities, such as graphical user interface (GUI) widgets.

22. Why there are no global variables in Java?

Global variables are globally accessible. Java does not support globally accessible variables due to following reasons:

1)The global variables breaks the referential transparency

2)Global variables creates collisions in namespace.

23. What are Encapsulation, Inheritance and Polymorphism?

Encapsulation is the mechanism that binds together code and data it manipulates and keeps both safe from outside interference and misuse. Inheritance is the process by which one object acquires the properties of another object. Polymorphism is the feature that allows one interface to be used for general class actions.

24. What is the use of bin and lib in JDK?

Bin contains all tools such as javac, appletviewer, awt tool, etc., whereas lib contains API and all packages.

25. What is method overloading and method overriding?

Method overloading: When a method in a class having the same method name with different arguments is said to be method overloading. Method overriding : When a method in a class having the same method name with same arguments is said to be method overriding.

26. What is the difference between this() and super()?

this() can be used to invoke a constructor of the same class whereas super() can be used to invoke a super class constructor.

27. What is Domain Naming Service(DNS)?

It is very difficult to remember a set of numbers(IP address) to connect to the Internet. The Domain Naming Service(DNS) is used to overcome this problem. It maps one particular IP address to a string of characters. For example, www. mascom. com implies com is the domain name reserved for US commercial sites, moscom is the name of the company and www is the name of the specific computer, which is mascom’s server.

28. What is URL?

URL stands for Uniform Resource Locator and it points to resource files on the Internet. URL has four components: http://www. address. com:80/index.html, where http - protocol name, address - IP address or host name, 80 - port number and index.html - file path.

29. What is RMI and steps involved in developing an RMI object?

Remote Method Invocation (RMI) allows java object that executes on one machine and to invoke the method of a Java object to execute on another machine. The steps involved in developing an RMI object are: a) Define the interfaces b) Implementing these interfaces c) Compile the interfaces and their implementations with the java compiler d) Compile the server implementation with RMI compiler e) Run the RMI registry f) Run the application.

30. What is RMI architecture?

RMI architecture consists of four layers and each layer performs specific functions: a) Application layer - contains the actual object definition. b) Proxy layer - consists of stub and skeleton. c) Remote Reference layer - gets the stream of bytes from the transport layer and sends it to the proxy layer. d) Transportation layer - responsible for handling the actual machine-to-machine communication.

Computer Architecture and Organization VIVA Questions And Answers:

1. What are the types of computer?
Personal computer, notebook computer, workstations, enterprise or mainframes.

2. What are the functional units of a computer?
Input unit, memory unit, arithmetic and logic unit, output unit and control unit.

3. What is a program?
A list of instructions that performs a task is called a program. Usually the program is stored in memory.

4. What is object program?
Compiling a high-level language source program in to a list of machine instructions constituting a machine language program is called an object program. It is the assembled machine language program.

5. What do you mean by bits?
Each number, character, or instruction is encoded as a string of binary digits called as bits, each having one of two possible values, 0 or 1.

6. Define RAM.
Memory in which any location can be reached in a short fixed time after specifying its address is called random-access memory ( RAM).

7. Define word length .
The number of bits in each word is often referred to as the word length of the computer. Typical word lengths range from 16 to 64 bits.

8. Define memory access time?
The time required to access one word is called as memory access time. This time is fixed and independent of the location of the word being accessed. It typically ranges from a few nanoseconds (ns) to about 100 ns for modern RAM units.

9. What is memory hierarchy?
The memory of a computer is normally implemented as a memory hierarchy of three or four levels of semiconductor RAM units with different speeds and sizes. The small, fast RAM units are called caches. The large and slowest unit is referred to as main memory.

10. What is primary storage and secondary storage?
Primary memory is a fast memory that operates at electronic speeds. It is expensive. Secondary memory is used when large amounts of data and many programs have to be stored, particularly for information that is accessed infrequently.

11. What are registers?
Registers are high speed storage elements. Each register can store one word of data. Access time to registers is faster than access time to the fastest cache memory.

12. What are timing signals?
Timing signals are generated by the control circuits. These are signals that determine when a given action should take place. Data transfers between the processor and memory are also controlled by the control unit through the timing signals.

13. Explain briefly the operation of Add LOCA, R0.
This instruction adds the operand at memory location LOCA to the operand in a register in the processor, R0, and places the sum in to register R0. The original contents of location LOCA are preserved, whereas those of R0 are overwritten.

14. What is instruction register?
The instruction register (IR) holds the instruction that is currently being executed. Its output is available to the control circuits which generate the timing signals that control the various processing elements involved in executing the instruction.

15. What is program counter?
The program counter (PC) keeps track of the execution of a program. It contains the memory address of the next instruction to be fetched and executed.

16. What is MAR and MDR?
The memory address register (MAR) holds the address of the location to be accessed. The memory data register (MDR) contains the data to be written into or read out of the addressed location.

17. What is an interrupt?
An interrupt is a request from an I/O device for service by the processor. The processor provides the requested service by executing an appropriate interrupt-service routine.

18. Define bus.
A group of lines that serves as a connecting path for several devices is called a bus. In addition to the lines that carry data, the bus must have lines for address and control purposes.

19. What is a compiler?
It is a system software program that translates the high-level language program into a suitable machine language program.

20. What is a text editor?
It is a system program used for entering and editing application programs.

21. What is a file?
A file is simply a sequence of alphanumeric characters or binary data that is stored in memory or in secondary storage. A file can be referred by a name chosen by the user.

22. Define OS.
Operating system (OS) is a large program, or a collection of routines, that is used to control the sharing of and interaction among various computer units as they execute application programs.

23. What is multiprogramming or multitasking?
The operating system manages the concurrent execution of several application programs to make the best possible use of computer resources. This pattern of concurrent execution is called multiprogramming or multitasking.

24. What is elapsed time?
It is a measure of performance of the entire computer system. It is affected by the speed of the processor, the disk and the printer.

25. What is processor time?
The sum of the periods during which the processor is active is called the processor time.

26. What are clock and clock cycles?
The timing signals that control the processor circuits are called as clocks. The clock defines regular time intervals called clock cycles.

27. Give the basic performance equation.
T = (N * S)/R
Where, T – performance parameter
N – actual number of instruction executions
S – average number of basic steps needed to execute one machine instruction
R – clock rate in cycles per second.

28. What is pipelining?
The technique of overlapping the execution of successive instruction for substantial improvement in performance is called pipelining.

29. What is superscalar execution?
In this type of execution, multiple functional units are used to create parallel paths through which different instructions can be executed in parallel. so it is possible to start the execution of several instructions in every clock cycle. This mode of operation is called superscalar execution.

30. What is RISC and CISC?
The processors with simple instructions are called as Reduced Instruction Set Computers(RISC). The processors with more complex instructions are called as Complex Instruction Set Computers (CISC).

31. Define SPEC rating.
Running time on the reference computer
SPEC rating = Running time on the computer under test

32. Define byte addressable memory.
Byte locations have addresses 0,1,2….Thus if the word length of the machine is 32 bits, successive words are located at addresses 0,4,8….with each word consisting of 4 bytes. This is called byte addressable memory.

33. What is big-endian and little-endian?
The name big-endian is used when lower byte addresses are used for the more significant bytes (the leftmost bytes) of the word. The name little-endian is used when lower byte addresses are used for the less significant bytes (the rightmost bytes) of the word.

34. What is aligned address?
Words are said to be aligned in memory if they begin at a byte address that is a multiple of the number of bytes in a word.

35. Explain briefly the operation of ‘load’.
The load operation transfers a copy of the contents of a specific memory location to the processor. The memory contents remain unchanged. To start a load operation, the processor sends the address of the
desired location to the memory and requests that its contents be read. The memory reads the data stored at that address and sends them to the processor.

36. Explain briefly the operation of ‘store’.
The store operation transfers an item of information from the processor to a specific memory location, destroying the former contents of that location. The processor sends the address of the desired location to the memory, together with the data to be written into that memory location.

37. What is register transfer notation?
R3 <- [R1] + [R2]
This type of notation is known as register transfer instruction (RTN). The right-hand side of an RTN expression always denotes a value, and the left-hand side is the name of a location where the value is to be placed, overwriting the old contents of that location.

38. What is a one address instruction?
The instruction that contains the memory address of only one operand is called one address instruction.
Eg. Load A, Store A.

39. What is a two address instruction?
The instruction that contains the memory address of two operands is called two byte address instruction.
Eg. Add A,B , Move B,C.

40. What is a three address instruction?
The instruction that contains the memory address of three operands is called three byte address instruction.
Eg. Add A,B,C.

41. What is a zero address instruction?
Instructions in which the locations of all operands are defined implicitly is called zero address instruction. Such instructions are found in machines that store operands in a structure called push down stack.

42. What is straight line sequencing?
To begin executing a program, the address of its first instruction must be placed into PC. Then the processor control circuits use the information in the PC to fetch and execute instructions, one at a time, in the order of increasing addresses. This is called straight line sequencing.

43. Define conditional branch.
A conditional branch instruction causes a branch only if a specified condition is satisfied. If the condition is not satisfied, the PC is incremented in the normal way and next instruction in the sequential address is
fetched and executed.

44. Define conditional code flags.
The processor keeps track of information about the results of various operations for use by subsequent conditional branch instructions. This is done by recording the required information in individual bits called as conditional code flags.

45. Define conditional code register (OR) status register.
The conditional code flags are usually grouped together in a special processor register called conditional code registers or status registers.

46. What are the four commonly used flags?
N (negative) – set to 1 if the result is negative; otherwise, cleared to 0
Z (zero)- set to 1 if the result is 0; otherwise, cleared to 0
V (overflow) – set to 1 if arithmetic overflow occurs; otherwise, cleared to 0
C (carry)- set to 1 if the carry-out results from the operation; otherwise, cleared to 0

47. What is addressing modes?
The different ways in which the location of a operand is specified in an instruction is referred to as addressing modes.

48. What are the various addressing modes?
Register mode, absolute mode, immediate mode, indirect mode, index mode, relative mode, auto increment mode, auto decrement mode.

49. Define register mode addressing.
In register mode addressing the operand is the contents of a process register. The name of the register is given in the instruction.

50. Define absolute mode addressing.
In absolute mode addressing the operand is in a memory location. The address of this location is given explicitly in the instruction. This is also called direct mode addressing.

51. Define immediate mode addressing.
In immediate mode addressing, the operand is given explicitly in the instruction.
Eg. Move #200,R0.

52. Define indirect mode addressing.
In indirect mode addressing the effective address of the operands is the content of a register or memory location whose address appears in the instruction.
Eg: Add (R2),R0.

53. What is a pointer?
The register or memory location that contains the address of an operand is called a pointer.
Eg: A= *B. Here B is a pointer variable.

54. Define index mode addressing.
In index mode addressing, the effective address of the operand is generated by adding a constant value to the register.
EA= X + [Ri].

55. Define relative mode addressing.
In relative mode addressing the effective address is determined by the index mode using the program counter in the place of the general purpose register Ri.

56. Define Auto increment mode .
In this mode the effective address of the operand is the contents of a register specified in the instruction. After accessing the operand, the contents of this register are automatically incremented to point to the next item in a list. It can be written as (Ri)+.

57. Define Auto decrement mode.
In this mode the contents of a register specified in the instruction are first automatically decremented and then used as the effective address of the operand. . It can be written as -(Ri).

58. What are mnemonics?
When writing programs for a specific computer, words such as Move, Add, Increment and Branch are replaced by acronyms such as MOV, ADD, INC and BR. This is called mnemonics.

59. What is an assembler?
Programs written in assembly language can be automatically translated in to a sequence of machine instructions by a program called an assembler.

60. What is a source program?
The user program in its original alphanumeric text format is called a source program.

61. What are assembler directives?
Consider the example SUM EQU 200. This statement does not denote an instruction that will be executed when the object program is run. This will not even appear in the object program. It simply informs the assembler that the name SUM should be replaced by the value 200 wherever it appears in
the program. Such statements are called assembler directives.

62. What is symbol table?
As the assembler scans through a source program, it keeps track of all names and the numeric values that correspond to them in a table called symbol table. Thus, when a name appears a second time, it is replaced with its value from the table.

63. What is a two pass assembler?
During the first pass of the assembler it creates a complete symbol table. At the end of this pass, all the names will be assigned numeric values. The assembler then goes through the source program second time and substitutes values for all names from the symbol table. Such an assembler is called a two-pass assembler.

64. What is a loader?
The assembler stores the object program on a magnetic disk. The object program must be loaded into the memory of the computer before it is executed. For this to happen, another utility program must already be loaded in the memory. This program is called a loader.

65. What is the use of debugger program?
The debugger program enables the user to stop execution of the object program at some points of interest and to examine the contents of various processor registers and memory locations.

66. What are device interface?
The buffer registers DATAIN and DATAOUT and the status flags SIN and SOUT are part of circuitry and they are commonly known as device interface.

67. Define memory mapped I/O.
Many computers use an arrangement called memory mapped I/O in which some memory address values are used to refer to peripheral device buffer registers, such as DATAIN and DATAOUT. This no special instructions are needed to access the contents of these registers.

68. What is a stack?
A stack is a list of data elements, usually words or bytes , with the accessing restriction that elements can be added or removed at one end of the list only. This end is called the top of the stack, and the other end is called the bottom of the stack.

69. Why is stack called as last-in-first-out?
Stack is called as last-in-first-out (LIFO), because the last data item placed on the stack is the first one removed when retrieval begins. The term push is used to describe placing a new item on the stack and pop is used to describe removing the top item from the stack.

70. What is a stack pointer?
Stack pointer (SP) is a processor register that is used to keep track of the address of the element of the stack that is at the top at any given time. It could be one of the general purpose registers or a register dedicated to this function.

71. What is a queue?
Queue is a data structure similar to the stack. Here new data are added at the back (high address end) and retrieved from the front (low address end) of the queue. Queue is also called as first-in-first-out (FIFO).

1. What is OOPS?
OOPS is abbreviated as Object Oriented Programming system in which programs are considered as a collection of objects. Each object is nothing but an instance of a class.

2. Write basic concepts of OOPS?
Following are the concepts of OOPS and are as follows:.

1. Abstraction.

2. Encapsulation.

3. Inheritance.

4. Polymorphism.

3. What is a class?
A class is simply a representation of a type of object. It is the blueprint/ plan/ template that describe the details of an object.

4. What is an object?
Object is termed as an instance of a class, and it has its own state, behavior and identity.

5. What is Encapsulation?
Encapsulation is an attribute of an object, and it contains all data which is hidden. That hidden data can be restricted to the members of that class.

6. What is Polymorphism?
Polymorphism is nothing butassigning behavior or value in a subclass to something that was already declared in the main class. Simply, polymorphism takes more than one form.

7. What is Inheritance?
Inheritance is a concept where one class shares the structure and behavior defined in another class. Ifinheritance applied on one class is called Single Inheritance, and if it depends on multiple classes, then it is called multiple Inheritance.

8. What are manipulators?
Manipulators are the functions which can be used in conjunction with the insertion (<<) and extraction (>>) operators on an object. Examples are endl and setw.

9. Define a constructor?
Constructor is a method used to initialize the state of an object, and it gets invoked at the time of object creation.

10. Define Destructor?
Destructor is a method which is automatically called when the object ismade ofscope or destroyed. Destructor name is also same asclass name but with the tilde symbol before the name.

11. What is Inline function?
Inline function is a technique used by the compilers and instructs to insert complete body of the function wherever that function is used in the program source code.

12. What is avirtual function?
Virtual function is a member function ofclass and its functionality can be overridden in its derived class. This function can be implemented by using a keyword called virtual, and it can be given during function declaration.Virtual function can be achieved in C++, and it can be achieved in C Language by using function pointers or pointers to function.

13. What isfriend function?

• Friend function is a friend of a class that is allowed to access to Public, private or protected data in that same class. If the function is defined outside the class cannot access such information.
• Friend can be declared anywhere in the class declaration, and it cannot be affected by access control keywords like private, public or protected.

14. What is function overloading?
Function overloading is defined as a normal function, but it has the ability to perform different tasks. It allows creation of several methods with the same name which differ from each other by type of input and output of the function.
Example:
void add(int& a, int& b);
void add(double& a, double& b);
void add(struct bob& a, struct bob& b);

15. What is operator overloading?
Operator overloading is a function where different operators are applied and depends on the arguments. Operator,-,* can be used to pass through the function , and it has their own precedence to execute.

Example:
class complex {
double real, imag;

public:
complex(double r, double i) :
real(r), imag(i) {}
complex operator+(complex a, complex b);
complex operator*(complex a, complex b);
complex& operator=(complex a, complex b);
}

a=1.2, b=6

16. What is an abstract class?
An abstract class is a class which cannot be instantiated. Creation of an object is not possible withabstract class , but it can be inherited. An abstract class can be contain members, methods and also Abstract method.

A method that is declared as abstract and does not have implementation is known as abstract method.

Syntax:
abstract void show(); //no body and abstract keyword

17. What is a ternary operator?
Ternary operator is said to be an operator which takes three arguments. Arguments and results are of different data types , and it is depends on the function. Ternary operator is also called asconditional operator.

18. What is the use of finalize method?
Finalize method helps to perform cleanup operations on the resources which are not currently used. Finalize method is protected , and it is accessible only through this class or by a derived class.

19. What are different types of arguments?
A parameter is a variable used during the declaration of the function or subroutine and arguments are passed to the function , and it should match with the parameter defined. There are two types of Arguments.
Call by Value – Value passed will get modified only inside the function , and it returns the same value whatever it is passed it into the function.
Call by Reference – Value passed will get modified in both inside and outside the functions and it returns the same or different value.

20. What is super keyword?
Super keyword is used to invoke overridden method which overrides one of its superclass methods. This keyword allows to access overridden methods and also to access hidden members of the super class.It also forwards a call from a constructor to a constructor in the super class.

21. What is method overriding?
Method overriding is a feature that allows sub class to provide implementation of a method that is already defined in the main class. This will overrides the implementation in the superclass by providing the same method name, same parameter and same return type.

22. What is an interface?
An interface is a collection of abstract method. If the class implements an inheritance, and then thereby inherits all the abstract methods of an interface.

23. What is exception handling?
Exception is an event that occurs during the execution of a program. Exceptions can be of any type – Run time exception, Error exceptions. Those exceptions are handled properly through exception handling mechanism like try, catch and throw keywords.

24. What are tokens?

1. Token is recognized by a compiler and it cannot be broken down into component elements. Keywords, identifiers, constants, string literals and operators are examples of tokens.

2. Even punctuation characters are also considered as tokens – Brackets, Commas, Braces and Parentheses.

25. Difference between overloading and overriding?

• Overloading is static binding whereas Overriding is dynamic binding. Overloading is nothing but the same method with different arguments , and it may or may not return the same value in the same class itself.
• Overriding is the same method names with same arguments and return types associates with the class and its child class.

26. Difference between class and an object?

• An object is an instance of a class. Objects hold any information , but classes don’t have any information. Definition of properties and functions can be done at class and can be used by the object.
• Class can have sub-classes, and an object doesn’t have sub-objects.

27. What is an abstraction?
Abstraction is a good feature of OOPS , and it shows only the necessary details to the client of an object. Means, it shows only necessary details for an object, not the inner details of an object. Example – When you want to switch On television, it not necessary to show all the functions of TV. Whatever is required to switch on TV will be showed by using abstract class.

28. What are access modifiers?
Access modifiers determine the scope of the method or variables that can be accessed from other various objects or classes. There are 5 types of access modifiers , and they are as follows:.

1. Private.

2. Protected.

3. Public.

4. Friend.

5. Protected Friend.

29. What is sealed modifiers?
Sealed modifiers are the access modifiers where it cannot be inherited by the methods. Sealed modifiers can also be applied to properties, events and methods. This modifier cannot be applied to static members.

30. How can we call the base method without creating an instance?
Yes, it is possible to call the base method without creating an instance. And that method should be,.Static method.Doing inheritance from that class.-Use Base Keyword from derived class.

31. What is the difference between new and override?
The new modifier instructs the compiler to use the new implementation instead of the base class function. Whereas, Override modifier helps to override the base class function.

32. What are the various types of constructors?
There are three various types of constructors , and they are as follows:.

- Default Constructor – With no parameters.
- Parametric Constructor – With Parameters. Create a new instance of a class and also passing arguments simultaneously.
- Copy Constructor – Which creates a new object as a copy of an existing object.

33. What is early and late binding?
Early binding refers to assignment of values to variables during design time whereas late binding refers to assignment of values to variables during run time.

34. What is ‘this’ pointer?
THIS pointer refers to the current object of a class. THIS keyword is used as a pointer which differentiates between the current object with the global object. Basically, it refers to the current object.

35. What is the difference between structure and a class?
Structure default access type is public , but class access type is private. A structure is used for grouping data whereas class can be used for grouping data and methods.
Structures are exclusively used for dataand it doesn’t require strict validation , but classes are used to encapsulates and inherit data which requires strict validation.

36. What is the default access modifier in a class?
The default access modifier of a class is Private by default.

37. What is pure virtual function?
A pure virtual function is a function which can be overridden in the derived classbut cannot be defined. A virtual function can be declared as Pure by using the operator =0.

Example - .
Virtual void function1() // Virtual, Not pure
Virtual void function2() = 0 //Pure virtual

38. What are all the operators that cannot be overloaded?
Following are the operators that cannot be overloaded -.

1. Scope Resolution (:: )

2. Member Selection (.)

3. Member selection through a pointer to function (.*)

39. What is dynamic or run time polymorphism?
Dynamic or Run time polymorphism is also known as method overriding in which call to an overridden function is resolved during run time, not at the compile time. It means having two or more methods with the same name,same signature but with different implementation.

40. Do we require parameter for constructors?
No, we do not require parameter for constructors.

41. What is a copy constructor?
This is a special constructor for creating a new object as a copy of an existing object. There will be always only on copy constructor that can be either defined by the user or the system.

42. What does the keyword virtual represented in the method definition?
It means, we can override the method.

43. Whether static method can use non static members?
False.

44. What arebase class, sub class and super class?

1. Base class is the most generalized class , and it is said to be a root class.

2. Sub class is a class that inherits from one or more base classes.

3. Super class is the parent class from which another class inherits.

45. What is static and dynamic binding?

1. Binding is nothing but the association of a name with the class. Static binding is a binding in which name can be associated with the class during compilation time , and it is also called as early Binding.

2. Dynamic binding is a binding in which name can be associated with the class during execution time , and it is also called as Late Binding.

46. How many instances can be created for an abstract class?
Zero instances will be created for an abstract class.

47. Which keyword can be used for overloading?
Operator keyword is used for overloading.

48. What is the default access specifier in a class definition?
Private access specifier is used in a class definition.

49. Which OOPS concept is used as reuse mechanism?
Inheritance is the OOPS concept that can be used as reuse mechanism.

50. Which OOPS concept exposes only necessary information to the calling functions?
Data Hiding / Abstraction

Computer Networks Viva Questions and Answers:

1. Define Network?
A network is a set of devices connected by physical media links. A network is recursively is a connection of two or more nodes by a physical link or two or more networks connected by one or more nodes.
2. What is a Link?
At the lowest level, a network can consist of two or more computers directly connected by some physical medium such as coaxial cable or optical fiber. Such a physical medium is called as Link.
3. What is a node?
A network can consist of two or more computers directly connected by some physical medium such as coaxial cable or optical fiber. Such a physical medium is called as Links and the computer it connects is called as Nodes.
4. What is a gateway or Router?
A node that is connected to two or more networks is commonly called as router or Gateway. It generally forwards message from one network to another.
5. What is point-point link?
If the physical links are limited to a pair of nodes it is said to be point-point link.
6. What is Multiple Access?
If the physical links are shared by more than two nodes, it is said to be Multiple Access.
7. What are the advantages of Distributed Processing?
a. Security/Encapsulation
b. Distributed database
c. Faster Problem solving
d. Security through redundancy
e. Collaborative Processing
8. What are the criteria necessary for an effective and efficient network?
a. Performance
It can be measured in many ways, including transmit time and response time. b. Reliability
It is measured by frequency of failure, the time it takes a link to recover from a failure, and the network's robustness.
c. Security
Security issues includes protecting data from unauthorized access and virues.
9. Name the factors that affect the performance of the network?
a. Number of Users
b. Type of transmission medium
c. Hardware
d. Software
10. Name the factors that affect the reliability of the network?
a. Frequency of failure
b. Recovery time of a network after a failure
11. Name the factors that affect the security of the network?
a. Unauthorized Access
b. Viruses
12. What is Protocol?
A protocol is a set of rules that govern all aspects of information communication.
13. What are the key elements of protocols?
The key elements of protocols are
a. Syntax
It refers to the structure or format of the data, that is the order in which they are presented.
b. Semantics
It refers to the meaning of each section of bits.
c. Timing
Timing refers to two characteristics: When data should be sent and how fast they can be sent.
14. What are the key design issues of a computer Network?
a. Connectivity
b. Cost-effective Resource Sharing
c. Support for common Services
d. Performance
15. Define Bandwidth and Latency?
Network performance is measured in Bandwidth (throughput) and Latency (Delay). Bandwidth of a network is given by the number of bits that can be transmitted over the network in a certain period of time. Latency corresponds to how long it t5akes a message to travel from one end off a network to the other. It is strictly measured in terms of time.
16. Define Routing?
The process of determining systematically hoe to forward messages toward the destination nodes based on its address is called routing.
17. What is a peer-peer process?
The processes on each machine that communicate at a given layer are called peer-peer process.
18. When a switch is said to be congested?
It is possible that a switch receives packets faster than the shared link can accommodate and stores in its memory, for an extended period of time, then the switch will eventually run out of buffer space, and some packets will have to be dropped and in this state is said to congested state.
19. What is semantic gap?
Defining a useful channel involves both understanding the applications requirements and recognizing the limitations of the underlying technology. The gap between what applications expects and what the underlying technology can provide is called semantic gap.
20. What is Round Trip Time?
The duration of time it takes to send a message from one end of a network to the other and back, is called RTT.
21. Define the terms Unicasting, Multiccasting and Broadcasting?
If the message is sent from a source to a single destination node, it is called Unicasting.
If the message is sent to some subset of other nodes, it is called Multicasting.
If the message is sent to all the m nodes in the network it is called Broadcasting.
22. What is Multiplexing?
Multiplexing is the set of techniques that allows the simultaneous transmission of multiple signals across a single data link.
23. Name the categories of Multiplexing?
a. Frequency Division Multiplexing (FDM)
b. Time Division Multiplexing (TDM)
i. Synchronous TDM
ii. ASynchronous TDM Or Statistical TDM.
c. Wave Division Multiplexing (WDM)
24. What is FDM?
FDM is an analog technique that can be applied when the bandwidth of a link is greater than the combined bandwidths of the signals to be transmitted.
25. What is WDM?
WDM is conceptually the same as FDM, except that the multiplexing and demultiplexing involve light signals transmitted through fiber optics channel.
26. What is TDM?
TDM is a digital process that can be applied when the data rate capacity of the transmission medium is greater than the data rate required by the sending and receiving devices.
27. What is Synchronous TDM?
In STDM, the multiplexer allocates exactly the same time slot to each device at all times, whether or not a device has anything to transmit.
28. List the layers of OSI
a. Physical Layer
b. Data Link Layer
c. Network Layer
d. Transport Layer
e. Session Layer
f. Presentation Layer
g. Application Layer
29. Which layers are network support layers?
a. Physical Layer
b. Data link Layer and
c. Network Layers
30. Which layers are user support layers?
a. Session Layer
b. Presentation Layer and
c. Application Layer
31. Which layer links the network support layers and user support layers?
The Transport layer links the network support layers and user support layers.
32. What are the concerns of the Physical Layer?
Physical layer coordinates the functions required to transmit a bit stream over a physical medium.
a. Physical characteristics of interfaces and media
b. Representation of bits
c. Data rate
d. Synchronization of bits
e. Line configuration
f. Physical topology
g. Transmission mode
33. What are the responsibilities of Data Link Layer?
The Data Link Layer transforms the physical layer, a raw transmission facility, to a reliable link and is responsible for node-node delivery.
a. Framing
b. Physical Addressing
c. Flow Control
d. Error Control
e. Access Control
34. What are the responsibilities of Network Layer?
The Network Layer is responsible for the source-to-destination delivery of packet possibly across multiple networks (links).
a. Logical Addressing
b. Routing
35. What are the responsibilities of Transport Layer?
The Transport Layer is responsible for source-to-destination delivery of the entire message.
a. Service-point Addressing
b. Segmentation and reassembly
c. Connection Control
d. Flow Control
e. Error Control
36. What are the responsibilities of Session Layer?
The Session layer is the network dialog Controller. It establishes, maintains and synchronizes the interaction between the communicating systems.
a. Dialog control
b. Synchronization
37. What are the responsibilities of Presentation Layer?
The Presentation layer is concerned with the syntax and semantics of the information exchanged between two systems.
a. Translation
b. Encryption
c. Compression
38. What are the responsibilities of Application Layer?
The Application Layer enables the user, whether human or software, to access the network. It provides user interfaces and support for services such as e-mail, shared database management and other types of distributed information services.
a. Network virtual Terminal
b. File transfer, access and Management (FTAM)
c. Mail services
d. Directory Services
39. What are the two classes of hardware building blocks?
Nodes and Links.
40. What are the different link types used to build a computer network?
a. Cables
b. Leased Lines
c. Last-Mile Links
d. Wireless Links
41. What are the categories of Transmission media?
a. Guided Media
i. Twisted - Pair cable
1. Shielded TP
2. Unshielded TP
ii. Coaxial Cable
iii. Fiber-optic cable
b. Unguided Media
i. Terrestrial microwave
ii. Satellite Communication
42. What are the types of errors?
a. Single-Bit error
In a single-bit error, only one bit in the data unit has changed
b. Burst Error
A Burst error means that two or more bits in the data have changed.
43. What is Error Detection? What are its methods?
Data can be corrupted during transmission. For reliable communication errors must be deducted and Corrected. Error Detection uses the concept of redundancy, which means adding extra bits for detecting errors at the destination. The common Error Detection methods are
a. Vertical Redundancy Check (VRC)
b. Longitudinal Redundancy Check (VRC)
c. Cyclic Redundancy Check (VRC)
d. Checksum
44. What is Redundancy?
The concept of including extra information in the transmission solely for the purpose of comparison. This technique is called redundancy.
45. What is VRC?
It is the most common and least expensive mechanism for Error Detection. In VRC, a parity bit is added to every data unit so that the total number of 1s becomes even for even parity. It can detect all single-bit errors. It can detect burst errors only if the total number of errors in each data unit is odd.
46. What is LRC?
In LRC, a block of bits is divided into rows and a redundant row of bits is added to the whole block. It can detect burst errors. If two bits in one data unit are damaged and bits in exactly the same positions in another data unit are also damaged, the LRC checker will not detect an error. In LRC a redundant data unit follows n data units.
47. What is CRC?
CRC, is the most powerful of the redundancy checking techniques, is based on binary division.
48. What is Checksum?
Checksum is used by the higher layer protocols (TCP/IP) for error detection
49. List the steps involved in creating the checksum.
a. Divide the data into sections
b. Add the sections together using 1's complement arithmetic
c. Take the complement of the final sum, this is the checksum.
50. What are the Data link protocols?
Data link protocols are sets of specifications used to implement the data link layer. The categories of Data Link protocols are 1. Asynchronous Protocols
2. Synchronous Protocols
a. Character Oriented Protocols
b. Bit Oriented protocols
51. Compare Error Detection and Error Correction:
The correction of errors is more difficult than the detection. In error detection, checks only any error has occurred. In error correction, the exact number of bits that are corrupted and location in the message are known. The number of the errors and the size of the message are important factors.
52. What is Forward Error Correction?
Forward error correction is the process in which the receiver tries to guess the message by using redundant bits.
53. Define Retransmission?
Re transmission is a technique in which the receiver detects the occurrence of an error and asks the sender to resend the message. Re sending is repeated until a message arrives that the receiver believes is error-freed.
54. What are Data Words?
In block coding, we divide our message into blocks, each of k bits, called datawords. The block coding process is one-to-one. The same dataword is always encoded as the same codeword.
55. What are Code Words?
"r" redundant bits are added to each block to make the length n = k + r. The resulting n-bit blocks are called codewords. 2n - 2k codewords that are not used. These codewords are invalid or illegal.
56. What is a Linear Block Code?
A linear block code is a code in which the exclusive OR (addition modulo-2) of two valid codewords creates another valid codeword.
57. What are Cyclic Codes?
Cyclic codes are special linear block codes with one extra property. In a cyclic code, if a codeword is cyclically shifted (rotated), the result is another codeword.
58. Define Encoder?
A device or program that uses predefined algorithms to encode, or compress audio or video data for storage or transmission use. A circuit that is used to convert between digital video and analog video.
59. Define Decoder?
A device or program that translates encoded data into its original format (e.g. it decodes the data). The term is often used in reference to MPEG-2 video and sound data, which must be decoded before it is output.
60. What is Framing?
Framing in the data link layer separates a message from one source to a destination, or from other messages to other destinations, by adding a sender address and a destination address. The destination address defines where the packet has to go and the sender address helps the recipient acknowledge the receipt.
61. What is Fixed Size Framing?
In fixed-size framing, there is no need for defining the boundaries of the frames. The size itself can be used as a delimiter.
62. Define Character Stuffing?
In byte stuffing (or character stuffing), a special byte is added to the data section of the frame when there is a character with the same pattern as the flag. The data section is stuffed with an extra byte. This byte is usually called the escape character (ESC), which has a predefined bit pattern. Whenever the receiver encounters the ESC character, it removes it from the data section and treats the next character as data, not a delimiting flag.
63. What is Bit Stuffing?
Bit stuffing is the process of adding one extra 0 whenever five consecutive Is follow a 0 in the data, so that the receiver does not mistake the pattern 0111110 for a flag.
64. What is Flow Control?
Flow control refers to a set of procedures used to restrict the amount of data that the sender can send before waiting for acknowledgment.
65. What is Error Control ?
Error control is both error detection and error correction. It allows the receiver to inform the sender of any frames lost or damaged in transmission and coordinates the retransmission of those frames by the sender. In the data link layer, the term error control refers primarily to methods of error detection and re transmission.
66. What Automatic Repeat Request (ARQ)?
Error control is both error detection and error correction. It allows the receiver to inform the sender of any frames lost or damaged in transmission and coordinates the retransmission of those frames by the sender. In the data link layer, the term error control refers primarily to methods of error detection and retransmission. Error control in the data link layer is often implemented simply: Any time an error is detected in an exchange, specified frames are retransmitted. This process is called automatic repeat request (ARQ).
67. What is Stop-and-Wait Protocol?
In Stop and wait protocol, sender sends one frame, waits until it receives confirmation from the receiver (okay to go ahead), and then sends the next frame.
68. What is Stop-and-Wait Automatic Repeat Request?
Error correction in Stop-and-Wait ARQ is done by keeping a copy of the sent frame and retransmitting of the frame when the timer expires.
69. What is usage of Sequence Number in Relaible Transmission?
The protocol specifies that frames need to be numbered. This is done by using sequence numbers. A field is added to the data frame to hold the sequence number of that frame. Since we want to minimize the frame size, the smallest range that provides unambiguous communication. The sequence numbers can wrap around.
70. What is Pipelining ?
In networking and in other areas, a task is often begun before the previous task has ended. This is known as pipelining.
71. What is Sliding Window?
The sliding window is an abstract concept that defines the range of sequence numbers that is the concern of the sender and receiver. In other words, he sender and receiver need to deal with only part of the possible sequence numbers.
72. What is Piggy Backing?
A technique called piggybacking is used to improve the efficiency of the bidirectional protocols. When a frame is carrying data from A to B, it can also carry control information about arrived (or lost) frames from B; when a frame is carrying data from B to A, it can also carry control information about the arrived (or lost) frames from A.
73. What are the two types of transmission technology available?
(i) Broadcast and (ii) point-to-point
74. What is subnet?
A generic term for section of a large networks usually separated by a bridge or router.
75. Difference between the communication and transmission.
Transmission is a physical movement of information and concern issues like bit polarity, synchronisation, clock etc.
Communication means the meaning full exchange of information between two communication media.
76. What are the possible ways of data exchange?
(i) Simplex (ii) Half-duplex (iii) Full-duplex.
77. What is SAP?
Series of interface points that allow other computers to communicate with the other layers of network protocol stack.
78. What do you meant by "triple X" in Networks?
The function of PAD (Packet Assembler Disassembler) is described in a document known as X.3. The standard protocol has been defined between the terminal and the PAD, called X.28; another standard protocol exists between hte PAD and the network, called X.29. Together, these three recommendations are often called "triple X".
79. What is frame relay, in which layer it comes?
Frame relay is a packet switching technology. It will operate in the data link layer.
80. What is terminal emulation, in which layer it comes?
Telnet is also called as terminal emulation. It belongs to application layer.
81. What is Beaconing?
The process that allows a network to self-repair networks problems. The stations on the network notify the other stations on the ring when they are not receiving the transmissions. Beaconing is used in Token ring and FDDI networks.
82. What is redirector?
Redirector is software that intercepts file or prints I/O requests and translates them into network requests. This comes under presentation layer.
83. What is NETBIOS and NETBEUI?
NETBIOS is a programming interface that allows I/O requests to be sent to and received from a remote computer and it hides the networking hardware from applications.
NETBEUI is NetBIOS extended user interface. A transport protocol designed by microsoft and IBM for the use on small subnets.
84. What is RAID?
A method for providing fault tolerance by using multiple hard disk drives.
85. What is passive topology?
When the computers on the network simply listen and receive the signal, they are referred to as passive because they don't amplify the signal in any way. Example for passive topology -linear bus.
86. What is Brouter?
Hybrid devices that combine the features of both bridges and routers.
87. What is cladding?
A layer of a glass surrounding the center fiber of glass inside a fiber-optic cable.
88. What is point-to-point protocol?
A communications protocol used to connect computers to remote networking services including Internet service providers.
89. How Gateway is different from Routers?
A gateway operates at the upper levels of the OSI model and translates information between two completely different network architectures or data formats.
90. What is attenuation?
The degeneration of a signal over distance on a network cable is called attenuation.
91. What is MAC address?
The address for a device as it is identified at the Media Access Control (MAC) layer in the network architecture. MAC address is usually stored in ROM on the network adapter card and is unique.
92. Difference between bit rate and baud rate.
Bit rate is the number of bits transmitted during one second whereas baud rate refers to the number of signal units per second that are required to represent those bits.
baud rate = (bit rate / N)
where N is no-of-bits represented by each signal shift.
93. What is Bandwidth?
Every line has an upper limit and a lower limit on the frequency of signals it can carry. This limited range is called the bandwidth.
94. What are the types of Transmission media?
Signals are usually transmitted over some transmission media that are broadly classified in to two categories.
a.) Guided Media: These are those that provide a conduit from one device to another that include twisted-pair, coaxial cable and fiber-optic cable. A signal traveling along any of these media is directed and is contained by the physical limits of the medium. Twisted-pair and coaxial cable use metallic that accept and transport signals in the form of electrical current. Optical fiber is a glass or plastic cable that accepts and transports signals in the form of light.
b.) Unguided Media: This is the wireless media that transport electromagnetic waves without using a physical conductor. Signals are broadcast either through air. This is done through radio communication, satellite communication and cellular telephony.
95. What is Project 802?
It is a project started by IEEE to set standards to enable intercommunication between equipment from a variety of manufacturers. It is a way for specifying functions of the physical layer, the data link layer and to some extent the network layer to allow for interconnectivity of major LAN protocols.
It consists of the following:
1. 802.1 is an internetworking standard for compatibility of different LANs and MANs across protocols.
2. 802.2 Logical link control (LLC) is the upper sublayer of the data link layer which is non-architecture-specific, that is remains the same for all IEEE-defined LANs.
3. Media access control (MAC) is the lower sublayer of the data link layer that contains some distinct modules each carrying proprietary information specific to the LAN product being used. The modules are Ethernet LAN (802.3), Token ring LAN (802.4), Token bus LAN (802.5).
4. 802.6 is distributed queue dual bus (DQDB) designed to be used in MANs.
96. What is Protocol Data Unit?
The data unit in the LLC level is called the protocol data unit (PDU). The PDU contains of four fields a destination service access point (DSAP), a source service access point (SSAP), a control field and an information field. DSAP, SSAP are addresses used by the LLC to identify the protocol stacks on the receiving and sending machines that are generating and using the data. The control field specifies whether the PDU frame is a information frame (I - frame) or a supervisory frame (S - frame) or a unnumbered frame (U - frame).
97. What are the different type of networking / internetworking devices?
1. Repeater: Also called a regenerator, it is an electronic device that operates only at physical layer. It receives the signal in the network before it becomes weak, regenerates the original bit pattern and puts the refreshed copy back in to the link.
2. Bridges: These operate both in the physical and data link layers of LANs of same type. They divide a larger network in to smaller segments. They contain logic that allow them to keep the traffic for each segment separate and thus are repeaters that relay a frame only the side of the segment containing the intended recipent and control congestion.
3. Routers: They relay packets among multiple interconnected networks (i.e. LANs of different type). They operate in the physical, data link and network layers. They contain software that enable them to determine which of the several possible paths is the best for a particular transmission.
4. Gateways: They relay packets among networks that have different protocols (e.g. between a LAN and a WAN). They accept a packet formatted for one protocol and convert it to a packet formatted for another protocol before forwarding it. They operate in all seven layers of the OSI model.
98. What is ICMP?
ICMP is Internet Control Message Protocol, a network layer protocol of the TCP/IP suite used by hosts and gateways to send notification of datagram problems back to the sender. It uses the echo test / reply to test whether a destination is reachable and responding. It also handles both control and error messages.
99. What are the data units at different layers of the TCP / IP protocol suite?
The data unit created at the application layer is called a message, at the transport layer the data unit created is called either a segment or an user datagram, at the network layer the data unit created is called the datagram, at the data link layer the datagram is encapsulated in to a frame and finally transmitted as signals along the transmission media.
100. What is difference between ARP and RARP?
The address resolution protocol (ARP) is used to associate the 32 bit IP address with the 48 bit physical address, used by a host or a router to find the physical address of another host on its network by sending a ARP query packet that includes the IP address of the receiver.
The reverse address resolution protocol (RARP) allows a host to discover its Internet address when it knows only its physical address.
101. What is the minimum and maximum length of the header in the TCP segment and IP datagram?
The header should have a minimum length of 20 bytes and can have a maximum length of 60 bytes.
102. What is the range of addresses in the classes of internet addresses?
Class A - 0.0.0.0 - 127.255.255.255
Class B - 128.0.0.0 - 191.255.255.255
Class C - 192.0.0.0 - 223.255.255.255
Class D - 224.0.0.0 - 239.255.255.255
Class E - 240.0.0.0 - 247.255.255.255
103. What is the difference between TFTP and FTP application layer protocols?
The Trivial File Transfer Protocol (TFTP) allows a local host to obtain files from a remote host but does not provide reliability or security. It uses the fundamental packet delivery services offered by UDP.
The File Transfer Protocol (FTP) is the standard mechanism provided by TCP / IP for copying a file from one host to another. It uses the services offer by TCP and so is reliable and secure. It establishes two connections (virtual circuits) between the hosts, one for data transfer and another for control information.
104. What are major types of networks and explain?
1. Server-based network: provide centralized control of network resources and rely on server computers to provide security and network administration
2. Peer-to-peer network: computers can act as both servers sharing resources and as clients using the resources.
105. What are the important topologies for networks?
1. BUS topology: In this each computer is directly connected to primary network cable in a single line.
Advantages: Inexpensive, easy to install, simple to understand, easy to extend.
2. STAR topology: In this all computers are connected using a central hub.
Advantages: Can be inexpensive, easy to install and reconfigure and easy to trouble shoot physical problems.
3. RING topology: In this all computers are connected in loop. Advantages: All computers have equal access to network media, installation can be simple, and signal does not degrade as much as in other topologies because each computer regenerates it.
106. What is mesh network?
A network in which there are multiple network links between computers to provide multiple paths for data to travel.
107. What is difference between baseband and broadband transmission?
In a baseband transmission, the entire bandwidth of the cable is consumed by a single signal. In broadband transmission, signals are sent on multiple frequencies, allowing multiple signals to be sent simultaneously.
108. Explain 5-4-3 rule?
In a Ethernet network, between any two points on the network ,there can be no more than five network segments or four repeaters, and of those five segments only three of segments can be populated.
109. What MAU?
In token Ring , hub is called Multistation Access Unit(MAU).
110. What is the difference between routable and non- routable protocols?
Routable protocols can work with a router and can be used to build large networks. Non-Routable protocols are designed to work on small, local networks and cannot be used with a router.
111. Why should you care about the OSI Reference Model?
It provides a framework for discussing network operations and design.
112. What is logical link control?
One of two sublayers of the data link layer of OSI reference model, as defined by the IEEE 802 standard. This sublayer is responsible for maintaining the link between computers when they are sending data across the physical network connection.
113. What is virtual channel?
Virtual channel is normally a connection from one source to one destination, although multicast connections are also permitted. The other name for virtual channel is virtual circuit.
114. What is virtual path?
Along any transmission path from a given source to a given destination, a group of virtual circuits can be grouped together into what is called path.
115. What is packet filter?
Packet filter is a standard router equipped with some extra functionality. The extra functionality allows every incoming or outgoing packet to be inspected. Packets meeting some criterion are forwarded normally. Those that fail the test are dropped.
116. What is traffic shaping?
One of the main causes of congestion is that traffic is often busy. If hosts could be made to transmit at a uniform rate, congestion would be less common. Another open loop method to help manage congestion is forcing the packet to be transmitted at a more predictable rate. This is called traffic shaping.
117. What is multicast routing?
Sending a message to a group is called multicasting, and its routing algorithm is called multicast routing.
118. What is region?
When hierarchical routing is used, the routers are divided into what we will call regions, with each router knowing all the details about how to route packets to destinations within its own region, but knowing nothing about the internal structure of other regions.
119. What is silly window syndrome?
It is a problem that can ruin TCP performance. This problem occurs when data are passed to the sending TCP entity in large blocks, but an interactive application on the receiving side reads 1 byte at a time.
120. What are Digrams and Trigrams?
The most common two letter combinations are called as digrams. e.g. th, in, er, re and an. The most common three letter combinations are called as trigrams. e.g. the, ing, and, and ion.

1.What is UML?

UML stands for the Unified Modeling Language.

It is a graphical language for 1) visualizing, 2) constructing, and 3) documenting the artifacts of a system.

It allows you to create a blue print of all the aspects of the system, before actually physically implementing the system.

2.What are the advantages of creating a model?
Modeling is a proven and well-accepted engineering technique which helps build a model.
Model is a simplification of reality; it is a blueprint of the actual system that needs to be built.
Model helps to visualize the system.
Model helps to specify the structural and behavior of the system.
Model helps make templates for constructing the system.
Model helps document the system.

3.What are the different views that are considered when building an object-oriented software system?
Normally there are 5 views.
Use Case view - This view exposes the requirements of a system.
Design View - Capturing the vocabulary.
Process View - modeling the distribution of the systems processes and threads.
Implementation view - addressing the physical implementation of the system.
Deployment view - focus on the modeling the components required for deploying the system.

4.What are the major three types of modeling used?
The 3 Major types of modeling are

1. architectural,

2. behavioral, and

3. structural.

5.Name 9 modeling diagrams that are frequently used?
9 Modeling diagrams that are commonly used are

1. Use case diagram

2. Class Diagram

3. Object Diagram

4. Sequence Diagram

5. statechart Diagram

6. Collaboration Diagram

7. Activity Diagram

8. Component diagram

9. Deployment Diagram.

6.How would you define Architecture?
Architecture is not only taking care of the structural and behavioral aspect of a software system but also taking into account the software usage, functionality, performance, reuse, economic and technology constraints.

7.What is SDLC (Software Development Life Cycle)?
SDLC is a system including processes that are
Use case driven,
Architecture centric,
Iterative, and
Incremental.

8.What is the Life Cycle divided into?
This Life cycle is divided into phases.

• Each Phase is a time span between two milestones.
• The milestones are
• Inception,
• Elaboration,
• Construction, and
• Transition.

9.What are the Process Workflows that evolve through these phases?
The Process Workflows that evolve through these phases are

1. Business Modeling,

2. Requirement gathering,

3. Analysis and Design,

4. Implementation,

5. Testing,

6. Deployment.

7. Supporting Workflows are Configuration, change management, and Project management.

10.What are Relationships?
There are different kinds of relationships:
Dependencies,
Generalization, and
Association.
Dependencies are relationships between two entities.
A change in specification of one thing may affect another thing.
Most commonly it is used to show that one class uses another class as an argument in the signature of the operation.

Generalization is relationships specified in the class subclass scenario, it is shown when one entity inherits from other.
Associations are structural relationships that are:
a room has walls,
Person works for a company.

Aggregation is a type of association where there is a has a relationship.
As in the following examples: A room has walls, or if there are two classes room and walls then the relation ship is called a association and further defined as an aggregation.

11.How are the diagrams divided?
The nine diagrams are divided into static diagrams and dynamic diagrams.

12.Static Diagrams (Also called Structural Diagram):
The following diagrams are static diagrams.

1. Class diagram,

2. Object diagram,

3. Component Diagram,

4. Deployment diagram.

13.Dynamic Diagrams (Also called Behavioral Diagrams):
The following diagrams are dynamic diagrams.

• Use Case Diagram,
• Sequence Diagram,
• Collaboration Diagram,
• Activity diagram,
• Statechart diagram.

14.What are Messages?
A message is the specification of a communication, when a message is passed that results in action that is in turn an executable statement.

15.What is an Use Case?
A use case specifies the behavior of a system or a part of a system.
Use cases are used to capture the behavior that need to be developed.
It involves the interaction of actors and the system.

Operating Systems VIVA Questions and Answers:

1.What is an operating system?
An operating system is a program that acts as an intermediary between the user and the computer hardware. The purpose of an OS is to provide a convenient environment in which user can execute programs in a convenient and efficient manner.It is a resource allocator responsible for allocating system resources and a control program which controls the operation of the computer h/w.

2.What are the various components of a computer system?
1. The hardware
2. The operating system
3. The application programs
4. The users.

3.What is purpose of different operating systems?
The machine Purpose Workstation individual usability &Resources utilization Mainframe Optimize utilization of hardware PC Support complex games, business application Hand held PCs Easy interface & min. power consumption

4.What are the different operating systems?
1. Batched operating systems
2. Multi-programmed operating systems
3. timesharing operating systems
4. Distributed operating systems
5. Real-time operating systems

6.What is a boot-strap program?
Bootstrapping is a technique by which a simple computer program activates a more complicated system of programs. It comes from an old expression "to pull oneself up by one's bootstraps."

7.What is BIOS?
A BIOS is software that is put on computers. This allows the user to configure the input and output of a computer. A BIOS is also known as firmware.

8.Explain the concept of the batched operating systems?
In batched operating system the users gives their jobs to the operator who sorts the programs according to their requirements and executes them. This is time consuming but makes the CPU busy all the time.

9.Explain the concept of the multi-programmed operating systems?
A multi-programmed operating systems can execute a number of programs concurrently. The operating system fetches a group of programs from the job-pool in the secondary storage which contains all the programs to be executed, and places them in the main memory. This process is called job scheduling. Then it chooses a program from the ready queue and gives them to CPU to execute. When a executing program needs some I/O operation then the operating system fetches another program and hands it to the CPU for execution, thus keeping the CPU busy all the time.

10.Explain the concept of the time sharing operating systems?
It is a logical extension of the multi-programmed OS where user can interact with the program. The CPU executes multiple jobs by switching among them, but the switches occur so frequently that the user feels as if the operating system is running only his program.

11.Explain the concept of the multi-processor systems or parallel systems?
They contain a no. of processors to increase the speed of execution, and reliability, and economy. They are of two types:
1. Symmetric multiprocessing
2. Asymmetric multiprocessing
In Symmetric multi processing each processor run an identical copy of the OS, and these copies communicate with each other as and when needed.But in Asymmetric multiprocessing each processor is assigned a specific task.

12.Explain the concept of the Distributed systems?
Distributed systems work in a network. They can share the network resources,communicate with each other

13.Explain the concept of Real-time operating systems?
A real time operating system is used when rigid time requirement have been placed on the operation of a processor or the flow of the data; thus, it is often used as a control device in a dedicated application. Here the sensors bring data to the computer. The computer must analyze the data and possibly adjust controls to
modify the sensor input.
They are of two types:
1. Hard real time OS
2. Soft real time OS
Hard-real-time OS has well-defined fixed time constraints. But soft real time operating systems have less stringent timing constraints.

14.Define MULTICS?
MULTICS (Multiplexed information and computing services) operating system was developed from 1965-1970 at Massachusetts institute of technology as a computing utility. Many of the ideas used in MULTICS were subsequently used in UNIX.

15.What is SCSI?
Small computer systems interface.

16.What is a sector?
Smallest addressable portion of a disk.

17.What is cache-coherency?
In a multiprocessor system there exist several caches each may containing a copy of same variable A. Then a change in one cache should immediately be reflected in all other caches this process of maintaining the same value of a data in all the caches s called cache-coherency.

18.What are residence monitors?
Early operating systems were called residence monitors.

19.What is dual-mode operation?
In order to protect the operating systems and the system programs from the malfunctioning programs the two mode operations were evolved:
1. System mode.
2. User mode.
Here the user programs cannot directly interact with the system resources, instead they request the operating system which checks the request and does the required task for the user programs-DOS was written for / intel 8088 and has no dual-mode. Pentium provides dual-mode operation.

20.What are the operating system components?
1. Process management
2. Main memory management
3. File management
4. I/O system management
5. Secondary storage management
6. Networking
7. Protection system
8. Command interpreter system

21.What are operating system services?
1. Program execution
2. I/O operations
3. File system manipulation
4. Communication
5. Error detection
6. Resource allocation
7. Accounting
8. Protection

22.What are system calls?
System calls provide the interface between a process and the operating system. System calls for modern Microsoft windows platforms are part of the win32 API, which is available for all the compilers written for Microsoft windows.

23.What is a layered approach and what is its advantage?
Layered approach is a step towards modularizing of the system, in which the operating system is broken up into a number of layers (or levels), each built on top of lower layer. The bottom layer is the hard ware and the top most is the user interface.The main advantage of the layered approach is modularity. The layers are
selected such that each uses the functions (operations) and services of only lower layer. This approach simplifies the debugging and system verification.

24.What is micro kernel approach and site its advantages?

• Micro kernel approach is a step towards modularizing the operating system where all nonessential components from the kernel are removed and implemented as system and user level program, making the kernel smaller.The benefits of the micro kernel approach include the ease of extending the operating system. All new services are added to the user space and consequently do not require modification of the kernel. And as kernel is smaller it is easier to upgrade it. Also this approach provides more security and reliability since most services are running as user processes rather than kernel’s keeping the kernel intact.

25.What are a virtual machines and site their advantages?

• It is the concept by which an operating system can create an illusion that a process has its own processor with its own (virtual) memory.
• The operating system implements virtual machine concept by using CPU scheduling and virtual memory.

1. The basic advantage is it provides robust level of security as each virtual machine is isolated from all other VM. Hence the system resources are completely protected.
2. Another advantage is that system development can be done without disrupting normal operation. System programmers are given their own virtual machine, and as system development is done on the virtual machine instead of on the actual
physical machine.
3. Another advantage of the virtual machine is it solves the compatibility problem.
EX: Java supplied by Sun micro system provides a specification for java virtual machine.

26.What is a process?
A program in execution is called a process. Or it may also be called a unit of work. A process needs some system resources as CPU time, memory, files, and i/o devices to accomplish the task. Each process is represented in the operating system by a process control block or task control block (PCB).Processes are of two types:
1. Operating system processes
2. User processes

27.What are the states of a process?
1. New
2. Running
3. Waiting
4. Ready
5. Terminated

28.What are various scheduling queues?
1. Job queue
2. Ready queue
3. Device queue

29.What is a job queue?
When a process enters the system it is placed in the job queue.

30.What is a ready queue?
The processes that are residing in the main memory and are ready and waiting to execute are kept on a list called the ready queue.

31.What is a device queue?
A list of processes waiting for a particular I/O device is called device queue.

32.What is a long term scheduler & short term schedulers?
Long term schedulers are the job schedulers that select processes from the job queue and load them into memory for execution. The short term schedulers are the CPU schedulers that select a process form the ready queue and allocate the CPU to one of them.

33.What is context switching?
Transferring the control from one process to other process requires saving the state of the old process and loading the saved state for new process. This task is known as context switching.

34.What are the disadvantages of context switching?
Time taken for switching from one process to other is pure over head. Because the system does no useful work while switching. So one of the solutions is to go for threading when ever possible.

35.What are co-operating processes?
The processes which share system resources as data among each other. Also the processes can communicate with each other via interprocess communication facility generally used in distributed systems. The best example is chat program used on the www.

36.What is a thread?
A thread is a program line under execution. Thread sometimes called a light-weight process, is a basic unit of CPU utilization; it comprises a thread id, a program counter, a register set, and a stack.

37.What are the benefits of multithreaded programming?
1. Responsiveness (needn’t to wait for a lengthy process)
2. Resources sharing
3. Economy (Context switching between threads is easy)
4. Utilization of multiprocessor architectures (perfect utilization of the multiple processors).

38.What are types of threads?
1. User thread
2. Kernel thread
User threads are easy to create and use but the disadvantage is that if they perform a blocking system calls the kernel is engaged completely to the single user thread blocking other processes. They are created in user space.Kernel threads are supported directly by the operating system. They are slower to create and manage. Most of the OS like Windows NT, Windows 2000, Solaris2, BeOS, and Tru64 Unix support kernel threading.

39.Which category the java thread do fall in?
Java threads are created and managed by the java virtual machine, they do not easily fall under the category of either user or kernel thread……

40.What are multithreading models?
Many OS provide both kernel threading and user threading. They are called multithreading models. They are of three types:
1. Many-to-one model (many user level thread and one kernel thread).
2. One-to-one model
3. Many-to –many
In the first model only one user can access the kernel thread by not allowing multi-processing. Example: Green threads of Solaris.The second model allows multiple threads to run on parallel processing systems. Creating user thread needs to create corresponding kernel thread (disadvantage).Example: Windows NT, Windows 2000, OS/2.The third model allows the user to create as many threads as necessary and the corresponding kernel threads can run in parallel on a multiprocessor.
Example: Solaris2, IRIX, HP-UX, and Tru64 Unix.

41.What is a P-thread?
P-thread refers to the POSIX standard (IEEE 1003.1c) defining an API for thread creation and synchronization. This is a specification for thread behavior, not an implementation. The windows OS have generally not supported the P-threads.

42.What are java threads?
Java is one of the small number of languages that support at the language level for the creation and management of threads. However, because threads are managed by the java virtual machine (JVM), not by a user-level library or kernel, it is difficult to classify Java threads as either user- or kernel-level.

43.What is process synchronization?
A situation, where several processes access and manipulate the same data concurrently and the outcome of the execution depends on the particular order in which the access takes place, is called race condition. To guard against the race condition we need to ensure that only one process at a time can be manipulating
the same data. The technique we use for this is called process synchronization.

44.What is critical section problem?
Critical section is the code segment of a process in which the process may be changing common variables, updating tables, writing a file and so on. Only one process is allowed to go into critical section at any given time (mutually exclusive).The critical section problem is to design a protocol that the processes can use to
co-operate. The three basic requirements of critical section are:
1. Mutual exclusion
2. Progress
3. bounded waiting
Bakery algorithm is one of the solutions to CS problem.

45.What is a semaphore?
It is a synchronization tool used to solve complex critical section problems. A semaphore is an integer variable that, apart from initialization, is accessed only through two standard atomic operations: Wait and Signal.

46.What is bounded-buffer problem?
Here we assume that a pool consists of n buffers, each capable of holding one item. The semaphore provides mutual exclusion for accesses to the buffer pool and is initialized to the value 1.The empty and full semaphores count the number of empty and full buffers, respectively. Empty is initialized to n, and full is initialized to 0.

47.What is readers-writers problem?
Here we divide the processes into two types:
1. Readers (Who want to retrieve the data only)
2. Writers (Who want to retrieve as well as manipulate)
We can provide permission to a number of readers to read same data at same time.But a writer must be exclusively allowed to access. There are two solutions to this problem:
1. No reader will be kept waiting unless a writer has already obtained permission to use the shared object. In other words, no reader should wait for other readers to complete simply because a writer is waiting.
2. Once a writer is ready, that writer performs its write as soon as possible. In other words, if a writer is waiting to access the object, no new may start reading.

48.What is dining philosophers’ problem?

• Consider 5 philosophers who spend their lives thinking and eating. The philosophers share a common circular table surrounded by 5 chairs, each belonging to one philosopher. In the center of the table is a bowl of rice, and the table is laid with five single chop sticks. When a philosopher thinks, she doesn’t interact with her colleagues.
• From time to time, a philosopher gets hungry and tries to pick up two chop sticks that are closest to her .A philosopher may pick up only one chop stick at a time. Obviously she can’t pick the stick in some others hand. When a hungry philosopher has both her chopsticks at the same time, she eats without releasing her chopsticks. When she is finished eating, she puts down both of her chopsticks and start thinking again.

49.What is a deadlock?
Suppose a process request resources; if the resources are not available at that time the process enters into a wait state. A waiting process may never again change state, because the resources they have requested are held by some other waiting processes. This situation is called deadlock.

50.What are necessary conditions for dead lock?
1. Mutual exclusion (where at least one resource is non-sharable)
2. Hold and wait (where a process hold one resource and waits for other resource)
3. No preemption (where the resources can’t be preempted)
4. circular wait (where p[i] is waiting for p[j] to release a resource. i= 1,2,…n
j=if (i!=n) then i+1
else 1 )

Digital Logic Design VIVA Questions and Answers:

1) Explain about setup time and hold time, what will happen if there is setup time and hold tine violation, how to overcome this?

Set up time is the amount of time before the clock edge that the input signal needs to be stable to guarantee it is accepted properly on the clock edge.
Hold time is the amount of time after the clock edge that same input signal has to be held before changing it to make sure it is sensed properly at the clock edge.
Whenever there are setup and hold time violations in any flip-flop, it enters a state where its output is unpredictable: this state is known as metastable state (quasi stable state); at the end of metastable state, the flip-flop settles down to either '1' or '0'. This whole process is known as metastability

2) What is skew, what are problems associated with it and how to minimize it?

In circuit design, clock skew is a phenomenon in synchronous circuits in which the clock signal (sent from the clock circuit) arrives at different components at different times.
This is typically due to two causes. The first is a material flaw, which causes a signal to travel faster or slower than expected. The second is distance: if the signal has to travel the entire length of a circuit, it will likely (depending on the circuit's size) arrive at different parts of the circuit at different times. Clock skew can cause harm in two ways. Suppose that a logic path travels through combinational logic from a source flip-flop to a destination flip-flop. If the destination flip-flop receives the clock tick later than the source flip-flop, and if the logic path delay is short enough, then the data signal might arrive at the destination flip-flop before the clock tick, destroying there the previous data that should have been clocked through. This is called a hold violation because the previous data is not held long enough at the destination flip-flop to be properly clocked through. If the destination flip-flop receives the clock tick earlier than the source flip-flop, then the data signal has that much less time to reach the destination flip-flop before the next clock tick. If it fails to do so, a setup violation occurs, so-called because the new data was not set up and stable before the next clock tick arrived. A hold violation is more serious than a setup violation because it cannot be fixed by increasing the clock period.
Clock skew, if done right, can also benefit a circuit. It can be intentionally introduced to decrease the clock period at which the circuit will operate correctly, and/or to increase the setup or hold safety margins. The optimal set of clock delays is determined by a linear program, in which a setup and a hold constraint appears for each logic path. In this linear program, zero clock skew is merely a feasible point.
Clock skew can be minimized by proper routing of clock signal (clock distribution tree) or putting variable delay buffer so that all clock inputs arrive at the same time

3) What is slack?

'Slack' is the amount of time you have that is measured from when an event 'actually happens' and when it 'must happen’.. The term 'actually happens' can also be taken as being a predicted time for when the event will 'actually happen'.
When something 'must happen' can also be called a 'deadline' so another definition of slack would be the time from when something 'actually happens' (call this Tact) until the deadline (call this Tdead).
Slack = Tdead - Tact.
Negative slack implies that the 'actually happen' time is later than the 'deadline' time...in other words it's too late and a timing violation....you have a timing problem that needs some attention.

4) What is glitch? What causes it (explain with waveform)? How to overcome it?

The following figure shows a synchronous alternative to the gated clock using a data path. The flip-flop is clocked at every clock cycle and the data path is controlled by an enable. When the enable is Low, the multiplexer feeds the output of the register back on itself. When the enable is High, new data is fed to the flip-flop and the register changes its state



5) Given only two xor gates one must function as buffer and another as inverter?

Tie one of xor gates input to 1 it will act as inverter.
Tie one of xor gates input to 0 it will act as buffer.

6) What is difference between latch and flipflop?

The main difference between latch and FF is that latches are level sensitive while FF are edge sensitive. They both require the use of clock signal and are used in sequential logic. For a latch, the output tracks the input when the clock signal is high, so as long as the clock is logic 1, the output can change if the input also changes. FF on the other hand, will store the input only when there is a rising/falling edge of the clock.

7) Build a 4:1 mux using only 2:1 mux?

8.Difference between heap and stack?

The Stack is more or less responsible for keeping track of what's executing in our code (or what's been "called"). The Heap is more or less responsible for keeping track of our objects (our data, well... most of it - we'll get to that later.).
Think of the Stack as a series of boxes stacked one on top of the next. We keep track of what's going on in our application by stacking another box on top every time we call a method (called a Frame). We can only use what's in the top box on the stack. When we're done with the top box (the method is done executing) we throw it away and proceed to use the stuff in the previous box on the top of the stack. The Heap is similar except that its purpose is to hold information (not keep track of execution most of the time) so anything in our Heap can be accessed at any time. With the Heap, there are no constraints as to what can be accessed like in the stack. The Heap is like the heap of clean laundry on our bed that we have not taken the time to put away yet - we can grab what we need quickly. The Stack is like the stack of shoe boxes in the closet where we have to take off the top one to get to the one underneath it.

9) Difference between mealy and moore state machine?

A) Mealy and Moore models are the basic models of state machines. A state machine which uses only Entry Actions, so that its output depends on the state, is called a Moore model. A state machine which uses only Input Actions, so that the output depends on the state and also on inputs, is called a Mealy model. The models selected will influence a design but there are no general indications as to which model is better. Choice of a model depends on the application, execution means (for instance, hardware systems are usually best realized as Moore models) and personal preferences of a designer or programmer

B) Mealy machine has outputs that depend on the state and input (thus, the FSM has the output written on edges)
Moore machine has outputs that depend on state only (thus, the FSM has the output written in the state itself.

Adv and Disadv
In Mealy as the output variable is a function both input and state, changes of state of the state variables will be delayed with respect to changes of signal level in the input variables, there are possibilities of glitches appearing in the output variables. Moore overcomes glitches as output dependent on only states and not the input signal level.
All of the concepts can be applied to Moore-model state machines because any Moore state machine can be implemented as a Mealy state machine, although the converse is not true.
Moore machine: the outputs are properties of states themselves... which means that you get the output after the machine reaches a particular state, or to get some output your machine has to be taken to a state which provides you the output.The outputs are held until you go to some other state Mealy machine:
Mealy machines give you outputs instantly, that is immediately upon receiving input, but the output is not held after that clock cycle.

10) Difference between onehot and binary encoding?

Common classifications used to describe the state encoding of an FSM are Binary (or highly encoded) and One hot.
A binary-encoded FSM design only requires as many flip-flops as are needed to uniquely encode the number of states in the state machine. The actual number of flip-flops required is equal to the ceiling of the log-base-2 of the number of states in the FSM.
A onehot FSM design requires a flip-flop for each state in the design and only one flip-flop (the flip-flop representing the current or "hot" state) is set at a time in a one hot FSM design. For a state machine with 9- 16 states, a binary FSM only requires 4 flip-flops while a onehot FSM requires a flip-flop for each state in the design
FPGA vendors frequently recommend using a onehot state encoding style because flip-flops are plentiful in an FPGA and the combinational logic required to implement a onehot FSM design is typically smaller than most binary encoding styles. Since FPGA performance is typically related to the combinational logic size of the FPGA design, onehot FSMs typically run faster than a binary encoded FSM with larger combinational logic blocks

11) How to achieve 180 degree exact phase shift?

Never tell using inverter
a) dcm’s an inbuilt resource in most of fpga can be configured to get 180 degree phase shift.
b) Bufgds that is differential signaling buffers which are also inbuilt resource of most of FPGA can be used.

12) What is significance of ras and cas in SDRAM?

SDRAM receives its address command in two address words.
It uses a multiplex scheme to save input pins. The first address word is latched into the DRAM chip with the row address strobe (RAS).
Following the RAS command is the column address strobe (CAS) for latching the second address word.
Shortly after the RAS and CAS strobes, the stored data is valid for reading.

13) Tell some of applications of buffer?

a)They are used to introduce small delays
b)They are used to eliminate cross talk caused due to inter electrode capacitance due to close routing.
c)They are used to support high fanout,eg:bufg


14) Implement an AND gate using mux?

This is the basic question that many interviewers ask. for and gate, give one input as select line,incase if u r giving b as select line, connect one input to logic '0' and other input to a.

15) What will happen if contents of register are shifter left, right?

It is well known that in left shift all bits will be shifted left and LSB will be appended with 0 and in right shift all bits will be shifted right and MSB will be appended with 0 this is a straightforward answer

What is expected is in a left shift value gets Multiplied by 2 eg:consider 0000_1110=14 a left shift will make it 0001_110=28, it the same fashion right shift will Divide the value by 2.

16)Given the following FIFO and rules, how deep does the FIFO need to be to prevent underflow or overflow?

RULES:
1) frequency(clk_A) = frequency(clk_B) / 4
2) period(en_B) = period(clk_A) * 100
3) duty_cycle(en_B) = 25%


Assume clk_B = 100MHz (10ns)
From (1), clk_A = 25MHz (40ns)
From (2), period(en_B) = 40ns * 400 = 4000ns, but we only output for
1000ns,due to (3), so 3000ns of the enable we are doing no output work. Therefore, FIFO size = 3000ns/40ns = 75 entries.

Mobile Application (Android) VIVA Questions and Answers:

1) What is Android?
It is an open-sourced operating system that is used primarily on mobile devices, such as cell phones and tablets. It is a Linux kernel-based system that’s been equipped with rich components that allows developers to create and run apps that can perform both basic and advanced functions.

2) What Is the Google Android SDK?
The Google Android SDK is a toolset that developers need in order to write apps on Android enabled devices. It contains a graphical interface that emulates an Android driven handheld environment, allowing them to test and debug their codes.

3) What is the Android Architecture?
Android Architecture is made up of 4 key components:
- Linux Kernel
- Libraries
- Android Framework
- Android Applications

4) Describe the Android Framework.
The Android Framework is an important aspect of the Android Architecture. Here you can find all the classes and methods that developers would need in order to write applications on the Android environment.

5) What is AAPT?
AAPT is short for Android Asset Packaging Tool. This tool provides developers with the ability to deal with zip-compatible archives, which includes creating, extracting as well as viewing its contents.

6) What is the importance of having an emulator within the Android environment?

The emulator lets developers “play” around an interface that acts as if it were an actual mobile device. They can write and test codes, and even debug. Emulators are a safe place for testing codes especially if it is in the early design phase.

7) What is the use of an activityCreator?
An activity Creator is the first step towards the creation of a new Android project. It is made up of a shell script that will be used to create new file system structure necessary for writing codes within the Android IDE.

8 ) Describe Activities.
Activities are what you refer to as the window to a user interface. Just as you create windows in order to display output or to ask for an input in the form of dialog boxes, activities play the same role, though it may not always be in the form of a user interface.

9) What are Intents?
Intents displays notification messages to the user from within the Android enabled device. It can be used to alert the user of a particular state that occurred. Users can be made to respond to intents.

10) Differentiate Activities from Services .
Activities can be closed, or terminated anytime the user wishes. On the other hand, services are designed to run behind the scenes, and can act independently. Most services run continuously, regardless of whether there are certain or no activities being executed.


11) What items are important in every Android project?
These are the essential items that are present each time an Android project is created:
- Android Manifest.xml
- build.xml
- bin/
- src/
- res/
- assets/

12) What is the importance of XML-based layouts?
The use of XML-based layouts provides a consistent and somewhat standard means of setting GUI definition format. In common practice, layout details are placed in XML files while other items are placed in source files.

13) What are containers?
Containers, as the name itself implies, holds objects and widgets together, depending on which specific items are needed and in what particular arrangement that is wanted. Containers may hold labels, fields, buttons, or even child containers, as examples.

14) What is Orientation?
Orientation, which can be set using set Orientation(), dictates if the Linear Layout is represented as a row or as a column. Values are set as either HORIZONTAL or VERTICAL.

15) What is the importance of Android in the mobile market?
Developers can write and register apps that will specifically run under the Android environment. This means that every mobile device that is Android enabled will be able to support and run these apps. With the growing popularity of Android mobile devices, developers can take advantage of this trend by creating and uploading their apps on the Android Market for distribution to anyone who wants to download it.

16) What do you think are some disadvantages of Android?
Given that Android is an open-source platform, and the fact that different Android operating systems have been released on different mobile devices, there’s no clear cut policy to how applications can adapt with various OS versions and upgrades.
--> One app that runs on this particular version of Android OS may or may not run on another version.
--> Another disadvantage is that since mobile devices such as phones and tabs come in different sizes and forms, it poses a challenge for developers to create apps that can adjust correctly to the right screen size and other varying features and specs.

17) What is adb?
Adb is short for "Android Debug Bridge". It allows developers the power to execute remote shell commands. Its basic function is to allow and control communication towards and from the emulator port.

18) What are the four essential states of an activity?
- Active – if the activity is at the foreground
- Paused – if the activity is at the background and still visible
- Stopped – if the activity is not visible and therefore is hidden or obscured by another activity
- Destroyed – when the activity process is killed or completed terminated

19) What is ANR?
ANR is short for Application Not Responding. This is actually a dialog that appears to the user whenever an application have been unresponsive for a long period of time.

20) Which elements can occur only once and must be present?
Among the different elements, the and elements must be present and can occur only once. The rest are optional, and can occur as many times as needed.


21) How are escape characters used as attribute?
Escape characters are preceded by double backslashes. For example, a newline character is created using ‘\\n’

22) What is the importance of settings permissions in app development?
Permissions allow certain restrictions to be imposed primarily to protect data and code. Without these, codes could be compromised, resulting to defects in functionality.

23) What is the function of an intent filter?
Because every component needs to indicate which intents they can respond to, intent filters are used to filter out intents that these components are willing to receive. One or more intent filters are possible, depending on the services and activities that is going to make use of it.

24) Enumerate the three key loops when monitoring an activity?
- Entire lifetime – activity happens between on Create and on Destroy
- Visible lifetime – activity happens between on Start and on Stop
- Foreground lifetime – activity happens between on Resume and on Pause

25) When is the on Stop() method invoked?
A call to on Stop method happens when an activity is no longer visible to the user, either because another activity has taken over or if in front of that activity.


26) Is there a case wherein other qualifiers in multiple resources take precedence over locale?
Yes, there are actually instances wherein some qualifiers can take precedence over locale. There are two known exceptions, which are the MCC (mobile country code) and MNC (mobile network code) qualifiers.

27) What are the different states wherein a process is based?
There are 4 possible states:
- foreground activity
- visible activity
- background activity
- empty process

28) How can the ANR be prevented?
One technique that prevents the Android system from concluding a code that has been responsive for a long period of time is to create a child thread. Within the child thread, most of the actual workings of the codes can be placed, so that the main thread runs with minimal periods of unresponsive times.

29) What role does Dalvik play in Android development?
Dalvik serves as a virtual machine, and it is where every Android application runs. Through Dalvik, a device is able to execute multiple virtual machines efficiently through better memory management.

30) What is the Android Manifest.xml?
This file is essential in every application. It is declared in the root directory and contains information about the application that the Android system must know before the codes can be executed.


31) What is the proper way of setting up an Android-powered device for app development?
The following are steps to be followed prior to actual application development in an Android-powered device:

-Declare your application as “debuggable” in your Android Manifest.
-Turn on “USB Debugging” on your device.
-Set up your system to detect your device.

32) Enumerate the steps in creating a bounded service through AIDL.
1. create the .aidl file, which defines the programming interface
2. implement the interface, which involves extending the inner abstract Stub class as well as implanting its methods.
3. expose the interface, which involves implementing the service to the clients.

33) What is the importance of Default Resources?
When default resources, which contain default strings and files, are not present, an error will occur and the app will not run. Resources are placed in specially named subdirectories under the project res/ directory.

34) When dealing with multiple resources, which one takes precedence?
Assuming that all of these multiple resources are able to match the configuration of a device, the ‘locale’ qualifier almost always takes the highest precedence over the others.

35) When does ANR occur?
The ANR dialog is displayed to the user based on two possible conditions. One is when there is no response to an input event within 5 seconds, and the other is when a broadcast receiver is not done executing within 10 seconds.


36) What is AIDL?
AIDL, or Android Interface Definition Language, handles the interface requirements between a client and a service so both can communicate at the same level through interprocess communication or IPC. This process involves breaking down objects into primitives that Android can understand. This part is required simply because a process cannot access the memory of the other process.

37) What data types are supported by AIDL?
AIDL has support for the following data types:
-string
-charSequence
-List
-Map
-all native Java data types like int,long, char and Boolean

38) What is a Fragment?
A fragment is a part or portion of an activity. It is modular in a sense that you can move around or combine with other fragments in a single activity. Fragments are also reusable.

39) What is a visible activity?
A visible activity is one that sits behind a foreground dialog. It is actually visible to the user, but not necessarily being in the foreground itself.

40) When is the best time to kill a foreground activity?
The foreground activity, being the most important among the other states, is only killed or terminated as a last resort, especially if it is already consuming too much memory. When a memory paging state has been reach by a foreground activity, then it is killed so that the user interface can retain its responsiveness to the user.


41) Is it possible to use or add a fragment without using a user interface?
Yes, it is possible to do that, such as when you want to create a background behavior for a particular activity. You can do this by using add(Fragment,string) method to add a fragment from the activity.

42) How do you remove icons and widgets from the main screen of the Android device?
To remove an icon or shortcut, press and hold that icon. You then drag it downwards to the lower part of the screen where a remove button appears.

43) What are the core components under the Android application architecture?
There are 5 key components under the Android application architecture:
- services
- intent
- resource externalization
- notifications
- content providers

44) What composes a typical Android application project?
A project under Android development, upon compilation, becomes an .apk file. This apk file format is actually made up of the AndroidManifest.xml file, application code, resource files, and other related files.

45) What is a Sticky Intent?
A Sticky Intent is a broadcast from sendStickyBroadcast() method such that the intent floats around even after the broadcast, allowing others to collect data from it.


46) Do all mobile phones support the latest Android operating system?
Some Android-powered phone allows you to upgrade to the higher Android operating system version. However, not all upgrades would allow you to get the latest version. It depends largely on the capability and specs of the phone, whether it can support the newer features available under the latest Android version.

47) What is portable wi-fi hotspot?
Portable Wi-Fi Hotspot allows you to share your mobile internet connection to other wireless device. For example, using your Android-powered phone as a Wi-Fi Hotspot, you can use your laptop to connect to the Internet using that access point.

48) What is an action?
In Android development, an action is what the intent sender wants to do or expected to get as a response. Most application functionality is based on the intended action.

49) What is the difference between a regular bitmap and a nine-patch image?
In general, a Nine-patch image allows resizing that can be used as background or other image size requirements for the target device. The Nine-patch refers to the way you can resize the image: 4 corners that are unscaled, 4 edges that are scaled in 1 axis, and the middle one that can be scaled into both axes.

50) What language is supported by Android for application development?
The main language supported is Java programming language. Java is the most popular language for app development, which makes it ideal even for new Android developers to quickly learn to create and deploy applications in the Android environment.

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