When you switch on your computer the following sequence of events occur:

• Firstly, the computer accesses instructions held in ROM that begin the startup process. These instructions are called the bootstrap loader.

• Next, the computer checks the various devices attached to the computer.

• Finally the computer accesses the hard disk to load and start running the Operating System.

The operating system, OS, is the special program needed to control how the computer and its peripheral devices work. The most common operating systems nowadays are the various versions of Microsoft Windows. Other OSes in use today include Unix/Linux and the MacOS.

Operating systems perform five main tasks:

The User Interface
The OS is responsible for displaying the Human Computer Interface (HCI) and for interpreting the commands issued by users. There are different ways of issuing instructions to the computer. Some OSes allow you to enter commands by typing instructions - these are called Command Driven Interfaces. Other OSes have a list of options that you can choose from - these are called Menu Driven Interfaces. The most common, however, are the OSes that use icons, menus, windows and a mouse to select. These are called Graphical User Interfaces.

Input/Output Management
It is possible to connect numerous devices to your computer system: printers, scanners, speakers, joysticks etc. It is the role of the operating system to handle communication between the processor and the various devices. Usually a software driver is needed, a special program that interprets

File Management
You can save and retrieve files on a number of backing storage devices: floppy disks, hard disks, CD-R, CD-RW and most recently, DVD-R. The operating system must keep a record of which files are stored where. This information is stored on a File Allocation Table (FAT).

Memory Management
Memory, more specifically, Random Access Memory (RAM) is used to hold data temporarily. It will hold sections of the operating system, any running programs and unsaved documents. The operating system is responsible for allocating the various sections of memory to these various purposes and protecting the contents of memory from being overwritten.

Process Management
At the very lowest level of the computer is the processor. The processor can only carry out one instruction at a time. Yet you can run several programs at one time. The operating system is responsible for deciding which task will be carried out by the processor.

Answer the following questions in your jotter.

1. Name five different versions of Microsoft Windows.

2. Why is there more than one version of Windows?

3. Find the recommended retail price for one version of Windows XP, Windows 2000, Mac OS and Unix.

4. Name and describe one example of a command driven interface.

5. Describe a program or situation where you have seen or used a command driven interface.

6. Why is the graphical user interface the most commonly used interface in modern computing?

7. Describe how each layer of the operating system will be used when you choose to open a MS Word document from a hard disk.

Go to Task 2
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