• The main purpose of the operating system is to allow the applications software to interact with the computer hardware
• Allows the computer hardware to behave in a predictable way so that the applications software can use it

Tasks it performs:

• Diagnostic checks: performs these checks when the computer is booted up
• controls the receipt of input devices such as the keyboard and mouse
• controls output: sends information to the screen or other output devices
• memory management: controls flow of data to and from the main processor
• works out where to store the data on the hard disk drive
• deals with security issues such as usernames and passwords

Brands of systems software:

• Linux
• Unix
• Mac OS-X
• Windows