iSOFT Sample Technical Placement Paper

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iSOFT Technical Latest Sample Placement Paper

1. What is a Real-Time System?

ANS: A real time process is a process that must respond to the events

within a certain time period. A real time operating system is an

operating system that can run real time processes successfully.

2.What is multiple inheritance (virtual inheritance)? What are its

advantages and disadvantages?

ANS: Multiple Inheritance is the process whereby a child can be derived

from more than one parent class. The advantage of multiple

inheritance is that it allows a class to inherit the functionality of morethan 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 (ambiguity) when two base classes implement a method with

the same name.

3. What is a Safe State and what is its use in deadlock avoidance?

ANS: When a process requests an available resource, system must

decide if immediate allocation leaves the system in a safe state. Systemis in safe state if there exists a safe sequence of all processes. Deadlock

Avoidance: ensure that a system will never enter an unsafe state.

4.What a derived class inherits or doesn't inherit?

ANS: Inherits: Every data member defined in the parent class (although

such members may not always be accessible in the derived class!)

Every ordinary member functions of the parent class (although such

members may not always be accessible in the derived class!)The same initial data layout as the base class. Doesn't Inherit :

The base class's constructors and destructor. The base class's

assignment operator.

The base class's friends.


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5. What is cache memory?

ANS: Cache memory is random access memory (RAM) that a computer

microprocessor can access more quickly than it can access regular RAM.As the microprocessor processes data, it looks first in the cache

memory and if it finds the data there (from a previous reading of data),

it does not have to do the more time-consuming reading of data from

larger memory.

6.When should you use multiple inheritance?

ANS: There are three acceptable answers:- "Never, Rarely," and

"When the problem domain cannot be accurately modeled any other

way." 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 a likely

and intuitive way to model this common problem domain. The

applicant 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.

7. What is Context Switch?

ANS: Switching the CPU to another process requires saving the state of

the old process and loading the saved state for the new process. This

task is known as a context switch. Context-switch time is pure

overhead, because the system does no useful work while switching. Itsspeed varies from machine to machine, depending on the memory

speed, the number of registers which must be copied, the existed of

special instructions(such as a single instruction to load or store all

registers).


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8.What is Pure Virtual Function? Why and when it is used?

ANS: The abstract class whose pure virtual method has to be

implemented by all the classes which derive on these. Otherwise it

would result in a compilation error. This construct should be used when

one wants to ensure that all the derived classes implement the method

defined as pure virtual in base class.

9. What is CPU Scheduler?

ANS: Selects from among the processes in memory that are ready to

execute, and allocates the CPU to one of them. CPU scheduling

decisions may take place when a process:

1. Switches from running to waiting state.2. Switches from running to ready state.

3. Switches from waiting to ready.

4. Terminates. Scheduling under 1 and 4 is non-preemptive. All other

scheduling is preemptive.

10.How can I handle a destructor that fails?

ANS: Write a message to a log-_le. But do not throw an exception. The

C++ rule is that you must never throw an exception from a destructor

that is being called during the "stack unwinding" process of another

exception.

For example: If someone says throw Foo (), the stack will be unwound

so all the stack frames between the throw Foo () and the} catch (Foo e)

{will get popped. This is called stack unwinding. During stack unwinding,

all the local objects in all those stack frames are destructed. If one of

those destructors throws an exception (say it throws a Bar object), the

C++ runtime system is in a no-win situation: should it ignore the Barand end up in the} catch (Foo e) {where it was originally headed?

Should it ignore the Foo and look for a} catch (Bare) {handler? There is

no good answer: either choice loses information. So the C++ language

guarantees that it will call terminate () at this point, and terminate ()

kills the process. Bang you're dead.


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11. What is Dispatcher?

ANS: Dispatcher module gives control of the CPU to the process

selected by the short-term scheduler; this involves: Switching context,

Switching to user mode, Jumping to the proper location in the user

program to restart that program, dispatch latency time it takes for the

dispatcher to stop one process and start another running.

12.What is Virtual Destructor?

ANS: Using virtual destructors, you can destroy objects without

knowing their type - the correct destructor for the object is invoked

using the virtual function mechanism. Note that destructors can also be

declared as pure virtual functions for abstract classes. if someone willderive from your class, and if someone will say "new Derived", where

"Derived" is derived from your class, and if someone will say delete p,

where the actual object's type is "Derived" but the pointer p's type is

your class.

13. What is DRAM? In which form does it store data?

ANS: DRAM is not the best, but its cheap, does the job, and is available

almost everywhere you look. DRAM data resides in a cell made of a

capacitor and a transistor. The capacitor tends to lose data unless its

recharged every couple of milliseconds, and this recharging tends to

slow down the performance of DRAM compared to speedier RAM

types.

14.How can I handle a constructor that fails?

ANS: Throw an exception. Constructors don't have a return type, so it's

not possible to use return codes. The best way to signal constructor

failure is therefore to throw an exception.15. Can a copy constructor accept an object of the same class as

parameter, instead of reference of the object?

ANS: No. It is specified in the definition of the copy constructor itself. It

should generate an error if a programmer specifies a copy constructor

with a first argument that is an object and not a reference.


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16. What is fragmentation? Different types of fragmentation?

ANS: Fragmentation occurs in a dynamic memory allocation system

when many of the free blocks are too small to satisfy any request.External Fragmentation: External Fragmentation happens when a

dynamic memory allocation algorithm allocates some memory and a

small piece is left over that cannot be effectively used. If too much

external fragmentation occurs, the amount of usable memory is

drastically reduced. Total memory space exists to satisfy a request, but

it is not contiguous. Internal Fragmentation: Internal fragmentation is

the space wasted inside of allocated memory blocks because of

restriction on the allowed sizes of allocated blocks. Allocated memorymay be slightly larger than requested memory; this size difference is

memory internal to a partition, but not being used.

17. What is hard disk and what is its purpose?

ANS: Hard disk is the secondary storage device, which holds the data in

bulk, and it holds the data on the magnetic medium of the disk. Hard

disks have a hard platter that holds the magnetic medium, the

magnetic medium can be easily erased and rewritten, and a typicaldesktop machine will have a hard disk with a capacity of between 10

and 40 gigabytes. Data is stored onto the disk in the form of files.

18.What is a "pure virtual" member function?

ANS: The abstract class whose pure virtual method has to be

implemented by all the classes which derive on these. Otherwise it

would result in a compilation error. This construct should be used when

one wants to ensure that all the derived classes implement the method

defined as pure virtual in base class.19. What is Extensible Stylesheet Language (XSL)?

ANS: XSL is a proposed styling language for formatting XML (extensible

Markup Language) documents. The proposal was submitted to the W3C

by Microsoft, Inso, and ArborText.


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20.How virtual functions are implemented C++?

ANS: Virtual functions are implemented using a table of function

pointers, called the vtable. There is one entry in the table per virtualfunction in the class. This table is created by the constructor of the

class. When a derived class is constructed, its base class is constructed

_rst which creates the vtable. If the derived class overrides any of the

base classes virtual functions, those entries in the vtable are

overwritten by the derived class constructor. This is why you should

never call virtual functions from a constructor: because the vtable

entries for the object may not have been set up by the derived class

constructor yet, so you might end up calling base class implementationsof those virtual functions.

21. What is the difference between Hard and Soft real-time systems?

ANS: A hard real-time system guarantees that critical tasks complete on

time. This goal requires that all delays in the system be bounded from

the retrieval of the stored data to the time that it takes the operating

system to finish any request made of it. A soft real time system where a

critical real-time task gets priority over other tasks and retains thatpriority until it completes. As in hard real time systems kernel delays

need to be bounded.

22.What are all the implicit member functions of the class? Or what are

all the functions which compiler implements for us if we don't define

one?

ANS: (a) default ctor

(b) copy ctor

(c) assignment operator(d) default destructor

(e) address operator

23. What is the important aspect of a real-time system or Mission

Critical Systems?


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ANS: A real time operating system has well defined fixed time

constraints. Process must be done within the defined constraints or the

system will fail. An example is the operating system for a flight control

computer or an advanced jet airplane. Often used as a control device in

a dedicated application such as controlling scientific experiments,

medical imaging systems, industrial control systems, and some display

systems. Real-Time systems may be either hard or soft real-time. Hard

real-time: Secondary storage limited or absent, data stored in short

term memory, or read-only memory (ROM), Conflicts with time-sharing

systems, not supported by general-purpose operating systems. Soft

real-time: Limited utility in industrial control of robotics, Useful inapplications (multimedia, virtual reality) requiring advanced operating-

system features.

24. What are the differences between a C++ struct and C++ class?

ANS: The default member and base class access specifies 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 specifes, member functions,

overloaded operators, and so on. 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 specified and private base-class

inheritance.

25. What is the state of the processor, when a process is waiting for

some event to occur?

ANS: Waiting state.

26.What is a container class? What are the types of container classes?

ANS: A container class is a class that is used to hold objects in memory

or external storage. A container class acts as a generic holder. A

container class has a predefined behavior and a well- known interface.


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A container class is a supporting class whose purpose is to hide the

topology used for maintaining the list of objects in memory. When a

container class contains a group of mixed objects, the container is

called a heterogeneous container; when the container is holding a

group of objects that are all the same, the container is called a

homogeneous container.

27. What is virtual memory?

ANS: Virtual memory is hardware technique where the system appears

to have more memory that it actually does. This is done by time-

sharing, the physical memory and storage parts of the memory one disk

when they are not actively being used.28.What is assignment operator?

ANS: Default assignment operator handles assigning one object to

another of the same class. Member to member copy (shallow copy).

29. What resources are used when a thread created? How do they

differ from those when a process is created?

ANS: When a thread is created the threads does not require any new

resources to execute the thread shares the resources like memory of

the process to which they belong to. The benefit of code sharing is that

it allows an application to have several different threads of activity all

within the same address space. Whereas if a new process creation is

very heavyweight because it always requires new address space to be

created and even if they share the memory then the inter process

communication is expensive when compared to the communication

between the threads.

30. What is the cause of thrashing? How does the system detectthrashing?

ANS: Once it detects thrashing, what can the system do to eliminate

this problem? - Thrashing is caused by under allocation of the minimum

number of pages required by a process, forcing it to continuously page


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fault. The system can detect thrashing by evaluating the level of CPU

utilization as compared to the level of multiprogramming. It can be

eliminated by reducing the level of multiprogramming.

31. What is Throughput, Turnaround time, waiting time and Response

time?

ANS: Throughput number of processes that complete their execution

per time unit. Turnaround time amount of time to execute a

particular process. Waiting time amount of time a process has been

waiting in the ready queue. Response time amount of time it takes

from when a request was submitted until the first response is

produced, not output (for time-sharing environment).32. While running DOS on a PC, which command would be used to

duplicate the entire diskette?

ANS: diskcopy

33.What is difference between malloc ()/free () and new/delete?

ANS: malloc allocates memory for object in heap but doesn't invoke

object's constructor to initialize the object. New allocates memory and

also invokes constructor to initialize the object. malloc() and free() donot support object semantics, does not construct and destruct objects

E.g. string * ptr = (string *)(malloc (sizeof(string))) Are not safe, and

does not calculate the size of the objects that it construct.

34. What is the difference between delete and delete []?

ANS: Whenever you allocate memory with new [], you have to free the

memory using delete []. When you allocate memory with 'new', then

use 'delete' without the brackets. You use new [] to allocate an array of

values (always starting at the index 0).35.What is Memory alignment??

ANS: The term alignment primarily means the tendency of an address

pointer value to be a multiple of some power of two. So a pointer with

two byte alignment has a zero in the least signi_cant bit. And a pointer


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with four byte alignment has a zero in both the two least signi_cant

bits. And so on. More alignment means a longer sequence of zero bits

in the lowest bits of a pointer.

36. What are the basic functions of an operating system?

ANS: Operating system controls and coordinates the use of the

hardware among the various applications programs for various uses.

Operating system acts as resource allocator and manager. Since there

are many possibly conflicting requests for resources the operating

system must decide which requests are allocated resources to

operating the computer system efficiently and fairly? Also operating

system is control program which controls the user programs to preventerrors and improper use of the computer. It is especially concerned

with the operation and control of I/O devices.

37.Can I use realloc () on pointers allocated via new?

ANS: No! When realloc () has to copy the allocation, it uses a bitwise

copy operation, which will tear many C++ objects to shreds. C++ objects

should be allowed to copy themselves.

They use their own copy constructor or assignment operator.

Besides all that, the heap that new uses may not be the same as the

heap that malloc () and realloc () use!

38. Why is it my ': hover declaration for links does not work?

ANS: Assuming you have already checked that your style sheet

declarations do conform to correct CSS syntax, it could be that you have

overlooked the importance of a correct order of style declarations for

links.

The CSS2 specification makes this following note on the importance ofplacing the dynamic pseudo-classes ': hover and ': active in correct

positions in a list of style declarations.

Note that the 'a: hover' must be placed after the 'a: link' and 'a: visited'

rules, since otherwise the cascading rules will hide the 'color' property


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of the 'a: hover' rule.

Similarly, because 'a: active' is placed after 'a: hover', the active color

will apply when the user both activates and hovers over the 'a'

element.

39. Document Style Semantics and Specification Language (DSSSL)?

ANS: Document Style Semantics and Specification Language is an

international standard, an expression language, a styling language for

associating processing (formatting and transformation) with SGML

documents, for example XML.

40. Why paging is used?

ANS: Paging is solution to external fragmentation problem which is to

permit the logical address space of a process to be noncontiguous, thus

allowing a process to be allocating physical memory wherever the latter

is available.

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