Operating System

(manages the hardware and running programs)

· load and manages processes

· provide interfaces to hardware via system calls

· provide a filesystem

· provide a basic user interface

Pre-emptive multitasking

1.CPU receives interrupt

2.interrupt stores program counter

3.interrupt invokes handler

4.handler saves rest of state of the CPU for the process

5.handler does its business

6.handler invokes the scheduler

7.scheduler selects a process to run

8.scheduler restores state of the CPU for that process

9.scheduler jumps execution to that process