Operating Systems : Multi-Tasking

A multi-tasking operating system is capable of appearing to carry out more than one task at a time.

Windows® 2000 and UNIX®; are examples of multi-tasking operating systems. If you have a computer with a multi-tasking OS you could be using a spreadsheet and a word processor at the same time. You could also have the computer testing every five minutes to see if you had any new email and displaying a television programme on screen. Most multi-tasking operating systems have a WIMP user interface with each task being displayed in its own window.

In reality because the computer only has one microprocessor it can only be doing one thing at once. The computer fools you into thinking it is doing more than one task at once by dividing the processor time up between each of the tasks. Each task is given a small amount of processor time in turn. The amount of time allocated to a task is known as a time slice. These time slices are very short, usually less that 1/1000 of a second. Because the slices are so small, the user is fooled into thinking that the computer is doing many things at once.

The time can be allocated to the different tasks on an equal basis (each tasks gets the same amount of time) or on a priority basis with more important or more urgent tasks getting most time. Commonly the task that the user is currently working on (such as entering data into a spreadsheet) has the highest priority. It is allowed exclusive use of the processor whenever it wants it and is known as the foreground job. Other less urgent tasks such as sending data to a printer are only permitted to use the processor when the foreground job does not need it. These tasks are known as background jobs.

If an operating system is carrying out more than one task then the job of allocating memory also becomes harder because the computer’s memory must be allocated between the tasks.

Multi-tasking operating systems are also sometimes known as multi-program operating systems.

Windows® 2000 is a registered trademark of Microsoft Corporation in the United States and other countries.

GCSE ICT Companion 04 - (C) P Meakin 2004