Operating System - Processes

Processes

Process Concept
Process Scheduling
Operation on Processes
Cooperating Processes
Interprocess Communication


Process Concept

An operating system executes a variety of programs:
Batch system – jobs
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:
program counter
stack
data section

Process States
As a process executes, it changes state
new: The process is being created.
running: Instructions are being executed.
waiting: The process is waiting for some event to occur.
ready: The process is waiting to be assigned to a process.
terminated: The process has finished execution.

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

Process Scheduling Queues

Job queue – set of all processes in the system.
Ready queue – set of all processes residing in main memory,ready and waiting to execute.
Device queues – set of processes waiting for an I/O device.
Process migration between the various queues.