Multitasking

Multitasking : Concurrent execution of multiple tasks/processes

 

Time multiplexing of CPU

-Creates impression of parallelism

-Even on single core/CPU system

 

Allows for asynchronous I/O

-I/O devices and CPU are truly parallel

-10ms waiting for HDD allows other processes to execute >10^10 instructions

 

Process context

-A process is (essentially) a program executing inside an OS

-Each running instances of a program (e.g., multiple browser windows) is a separate process

-Each process has a context 

   • Instruction counter

   • Values in registers, stack and heap

   • Resource handles (device access, open files)

 

Process management

- Processes need resources: CPU time, Memory, etc.

-Operating system manages processes:

   • Starts processes

   • Terminates processes (frees resources)

   • Controls resource usage (prevents monopolizing CPU time)

   • Schedules CPU time

   • Synchronizes processes if necessary

   • Allows for inter process communication