Context Switch
A running process may be interrupted and the operating
system assigns another process to the running state and turns control over that.
Switching of CPU to another process requires saving the state of old process
and loading the saved state for new process this task is known as context
switch.
The context of a process is represented in the PCB of a
process. It includes the value of a CPU registers, process state, memory
management information etc.
Context switch time is pure overhead because system does not
do any useful work while switching.
The possible events that may cause switching are-
It is due to some event that
is external to process. For example
1.
Clock interrupt
2.
I/O interrupt
3.
Memory interrupt
·
Trap
It relates
to an error or exception condition generated within currently running process
such as illegal file access attempt.
·
Supervisor call
A supervisor
call may marked from the program being executed .this call generates system
call use of system call places the process in blocked state.
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