1. 1 AQA ICT AS Level © Nelson Thornes 2008 Operating Systems What are they and why do we need them?

2. 2 AQA ICT AS Level © Nelson Thornes 2008 What is an operating system? When people use a computer, they usually want to do something using applications software, such as a word processor or even a computer game. Applications software will not run without systems software being installed. For example, operating system software makes all the electronic parts work together as a computer.

3. 3 AQA ICT AS Level © Nelson Thornes 2008 Functions of an operating system The operating system controls the system hardware. It is responsible for: booting up the system when the computer is first switched on managing memory during multi-tasking allocating processor time between tasks controlling where data is stored on disk communicating with input and output devices handling errors, system security, user and file permissions.

4. 4 AQA ICT AS Level © Nelson Thornes 2008 Communication The operating system needs to: interface with peripherals such as a mouse or printer handle interrupts – signals that need an immediate response, such as a mouse click to stop a file printing. Right! What do I have to send?

5. 5 AQA ICT AS Level © Nelson Thornes 2008 Handling storage The operating system organises the storage and retrieval of data files from backing storage such as the hard drive. It keeps a directory of where the files are stored on disk. It keeps track of the free space on the drive so that files can be stored efficiently for faster retrieval. Now where did I put that?

6. 6 AQA ICT AS Level © Nelson Thornes 2008 Memory management Ok, what shall I do next? While computers seem to be able to multitask, a single processor can only do one thing at a time. Dual and quad core processors behave as if the computer has more than one processor. The operating system allocates processing time and memory to the various tasks that need to be carried out.

7. 7 AQA ICT AS Level © Nelson Thornes 2008 Types of interface The operating system also provides the user different interfaces, such as: Graphical User Interface Command Line Interface Menu Driven Interface

8. 8 AQA ICT AS Level © Nelson Thornes 2008 Utilities The operating system may have some utilities such as file management software already built in. Other systems software, such as anti-virus software and firewalls, may need to be purchased separately.