Process and PCB

A process is an instant of program in execution. It will need certain resources like Input/output devices, processor and memory to accomplish its task. It is smallest unit of work individually scheduled by an operating system.

In operating system each process is represented by a PCB. It is a data structure physically represents a process in memory. It contains many process of information: -

     1.     Process state: -     When a process comes in execution it changes its state. The state of a process is defined by its current activity. Each process may be in one of following states during its execution. These states are New,  Ready,  Waiting, Running, Terminated.

     2.     Program counter: -     The counter indicates the address of the next instruction to be executed for this process.

     3.     CPU registers: -     The registers vary in number, size and type depending upon the computer architecture. They include accumulators, index registers, flag, stag pointer and other general purpose registers.

     4.     CPU scheduling information:-     This information includes a process priority pointer to scheduling queue and any other scheduling parameter.

     5.     Memory management information: -     This information involves/includes the value of base and limit registers, the page or segment tables, depending upon the memory management scheme used by the operating system.

     6.     Accounting information: -     This information includes the amount of CPU and real time used, time limits, account numbers, job on process numbers and so on.

     7.     Input/output information: -     This information includes the list if Input/output device allocated to this process, a list of open files and so on.

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