Process Concept


 An operating system executes a variety of programs:

      1.  Batch system jobs

      2. Time-shared systems user programs or tasks

Textbook uses the terms job and process almost  interchangeably.

Process a program in execution; process execution must progress in sequential fashion.

A process includes:

      1.  program counter

      2.  stack

      3. data section


Process State


As a process executes, it changes state

      1.  new: The process is being created.

      2. running: Instructions are being executed.

      3. waiting: The process is waiting for some event to occur.

      4. ready: The process is waiting to be assigned to a process.

      5. terminated: The process has finished execution.


Diagram of Process State





Process Control Block (PCB)




Information associated with each process.

Process state

Program counter

CPU registers

CPU scheduling information

Memory-management information

Accounting information

I/O status information


CPU Switch From Process to Process