2. Purpose of scheduling

Scheduling: the task of allocating CPU processor time amongst all running programs.

There are many reasons to have the operating system actively manage scheduling. This is done by software within the operating system called a 'scheduler'.

The scheduler ensures that the computer:

• Processes as many tasks as possible in a given time
• Makes maximum use of CPU time
• It will try to minimise the delay between when the user requests something to be done and when that task is completed.
• Makes maximum use of resources such as input-output devices
• Is able to prioritise jobs
• It will ensure that no task is left uncompleted for too long, even if they are low priority
• Is able to alter priorities according to need

As you can see in the list above, the scheduler has many duties to fulfill.

The ideal scheduler would be one that is making 100% use of the CPU, no jobs are left hanging around and the user is never aware of a time delay also no resources are left idle if a process is wanting to use it.

There are many scheduling algorithms that seek to accomplish this, and we will discuss some of them in the following pages.