Saturday, November 03, 2007

Guide to Operation System Part 1

Definition of Operation System (OS)
Definition: OS is a program that acts as an intermediary between user and computer hardware. It provides an environment in which user can run programs in a convenient and efficient manner but provides no useful function by itself (Note: OS is a pure overhead of real work).


Types of Software
Application Software: It is intended to solve a specific problem or provides generic tools to end users

System Software: It provides a general programming environment where programmers can create specific application.


OS seen as Resource Manager
-An OS creates resource abstraction
Resource abstraction is when OS hides the actual tasks needed to manage and use resources by providing simpler commands to access these resources. However this simplified usage limits flexibility.

-An OS manages resource sharing
There are two kinds of sharing, the first kind is Space-multiplex sharing and the second kind is Time-multiplex sharing.

Space-multiplex sharing is achieved by dividing a resource into two or more distinct units and allocates each to a different process.

Time-multiplex sharing is achieved by allocating an entire resource to a process for a period of time. E.g. CPU

Resource isolation is a technique which prevents unauthorized access of resources in a process by another process. E.g. RAM

Multiprogramming is a technique for sharing of CPU among runnable processes.However it does not improve any single process’s performance but can improve the overall system performance.

Multiprogramming Performance
Maximum(t1,t2…,tn) When overlap nicely
T > Maximum(t1,t2…,tn) When does not overlap nicely but with a number overlaps
T < t1+t2+…+tn When does not overlap nicely

Posted by Zack at 6:13 PM