process model





The software and large program is organized into a number of sequential processes or process. A process is just executing program including current values of the program counter, register and variables. Each process has its virtual CPU. The CPU switches back and forth from process to process.
Suppose four programs running in pseudo parallelism and CPU swit5ches from one program to another as shown in figures below:

One program counter process switch

One program counter process switch

 

Programs Counter Switch

Programs Counter Switch

 

Process Arival

Process Arival

From figure (a) four program are in memory in figure (b) them are four processes, each its own flow of control and each one running independently of the other once. Find in figure (c) , for long enough line all the process are running simultaneously, but at any given instant only one process is actually running.
The time required to execute a process is not same for all processes in CPU. Therefore, timing assumption of all process is not considered. Some process may require less time but some other may be require large time. This, control jump to another process after completing one process.



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