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