Q1 
A)What is an operating system? 
B)Identify the main Development in operating systems for desktops
computers in past 8 years?
C)Critically evaluate different operating systems after you have
identified them in 1B.
 
The answers should up to three A4 pages long.

Hi nishanthy

 I wonder why the length is specified. If there is a website
 which answers the question, would not a link be sufficient,
 without paraphrasing the info?

 It may help to indicate the level of expertise. Even if this
 is a school assignmet, what grade level or degree of expertise
 is assumed on reader's side?

   For newbies (and who else would ask what an OS is?)
 the most informative expose I ever saw is this famous parable:
http://www.motogrrl.com/humor/OS_airline.html

I do not know how to fill 3A4s, so I am posting it as a comment.
I hope you will nevertheless find it useful, or at least a bit
amusing. Hopefuly both.

Hedgie