The Systems Unit is the heart of the computer system.

It contains a number of components including the main computer circuit board commonly referred to as the motherboard. The motherboard contains the main computer-processing chip together with a series of RAM chips.

The unique aspect of the IBM personal computer was its open architecture. The IBM developers decided that they would allow other devices to be installed in their computers if the users required.

As a consequence the motherboard of the computer contained several slots that allowed additional circuit boards to be plugged into them.

This practice has continued through to today and all IBM-compatible computers feature special slots on the motherboard which allow you to plug additional circuit boards into the computer. These additional boards, sometimes referred to as daughter boards, are used to control floppy and hard disk drives, the monitor’s performance, colour, and resolution, printers, joysticks, modems, backup drives, fax cards, and a range of other computer-related peripheral equipment.

These daughter boards often required cables to be connected to them for equipment that may be placed outside of the systems unit. For example the card that controls the monitor obviously needs to be connected in some way to the screen. This is achieved through special cutout panels at the back of the computer.

If you look at the back of your computer you will see a series of cutout panels. Some have sockets in them used to connect external equipment. Although it is not really important for you to know at this point what they all do it is important to know that they do exist.

As mentioned earlier the computer differs from a calculator in its ability to store data.

When you wish to store data so that you can retrieve it again later even after the computer has been switched off you must store it on a disk.

There are three main forms of disk storage available: floppy disk, hard disk, and compact disk.

Floppy disks drives were built into the first IBM Personal Computer that rolled off the production line in 1981 and have continued ever since.

Originally the floppy disks were encased in a vinyl jacket which was easily bent and twisted (hence the name floppy). These disks were 5¼ inches in diameter.

From about 1987 onwards a more robust plastic casing was used and the disk size was reduced to 3½ inches in diameter.

The most popular form of disk today is the 3½-inch high density disk which has a capacity of about 1.44 MB - this would hold an A4 book of text about 500 pages in length!

Floppy disks are normally inserted into the computer through a disk drive located at the front or side of the systems unit.

Very soon after 1981 it was realised that floppy disk capacity was far too small for the types of applications being used on computers. Computer manufacturers turned to hard disks as an alternative storage medium for data.

Conceptually hard disks work the same as floppy disks. The main difference is that hard disks are built into the computer.

Because hard disks are inbuilt the engineering of them is much more precise than a floppy disk and they can therefore be designed in a way, which allows a much greater capacity and a much faster access rate than is possible on a floppy disk.

Hard disk capacities are therefore measured in megabytes and even gigabytes. An average hard disk capacity at the time of writing is about 500 megabytes - about 330 3½-inch high-density disks, or 1,390 of the original 5¼-inch floppy disks!

Until about 1990 hard disks were considered an optional extra. Because of the sophistication of modern software hard disks have now become a necessary piece of equipment on computers.

The third type of storage medium is compact disk. Computer compact disks are identical to music CDs in size and shape. They require a compact disk player either built in or connected to the computer.

Compact disks hold megabytes of data and are a very efficient means of storing large amounts of data.

At present compact disks are available only with software and data already stored on them. This is because the equipment to store data on a compact disk is very expensive and beyond the scope of most computer users to purchase.

Compact disks are used for providing you with information such as telephone books, encyclopaedias, dictionaries, mailing lists, pictures, sounds, and even software packages.

Your computer is capable of working with a number of other devices. The main ones are a mouse, a printer, and a modem.

A mouse is used as any easy way of selecting objects that appear on the screen. It consists of a plastic case with two or three buttons on top.

As you roll the mouse around on the desk a pointer moves about the computer screen. The idea with the mouse is that you use it to move the pointer on the screen on to a particular object that you wish to work with. You can then click, or sometimes double click, the mouse button to tell the computer to choose that object.

Today the mouse is an indispensable part of the computer.

Printers are necessary if you wish to produce paper copies of your work. There are basically three types of printers available: dot matrix, ink jet, and laser.

Dot matrix printers work a little like typewriters which have a ribbon. A print head, consisting of pins, strikes the paper via a ribbon. The pins are projected so as to forms letters of the alphabet or numbers. The heads can contain 9 or 24 pins - the clarity of the printing is enhanced with more pins.

Dot matrix printers are now gradually disappearing. They are relatively slow and are noisy to operate.

Ink jet printers squirt tiny jets of ink on to the paper. The jets are shaped to form letters or numbers and can even print picture images as well.

Ink jet printers are taking over from dot matrix printers and are very quiet and efficient.

The only problem with them is the high cost of the ink cartridges. Also to obtain peak performance you should use paper specially formulated for this type of printing - and, you guessed it, this is going to be more costly than ordinary paper.

Laser printers are the most expensive printers to purchase, but provide the fastest operation.

A laser printer works much the same as a photocopier where the print image is actually photographed on to the paper. A light-sensitive drum is used to transfer the image using toner to reproduce it on the paper.

Laser printers are ideal for high volume printing tasks such as letters and reports and are almost indispensable in an office. They are very quiet in operation.

Modems allow you to use the telephone network to connect to other computers outside of your immediate location. This is done so that you can transfer data between your computer and that of another person, or to access remote services such as the Internet.

Modems translate your computer data into a format so that it can be transmitted via the telephone communications network.

With recent advances in this technology it is possible to communicate with people across the world and to easily transfer data from one location to another.

Modems are a necessary piece of equipment if you wish to use services such as the Internet. The Internet (an acronym for International Network) is simply a worldwide maze of computers that are interconnected via the telephone communications network. The Internet allows you to search for topics of interest (for example, your children may need information for a project on endangered species), buy products, talk to overseas computer users, send messages (sometimes referred to as electronic mail), and more.

By now you might be getting a little confused between the terms hardware and software.

Hardware is used to refer to the physical parts of the computer: the systems units, the monitor, the keyboard, the mouse, the printer, are all hardware items.

Software is used to refer to the instructions that make the computer do something for you. Software falls into three broad categories: operating system, application, and programming.

Every computer must have an operating system. It is the operating system that allows the computer to communicate with the devices that are attached to it such as the printer, the disk drives, a modem, a mouse, and the like.

Application software is the real business end of computing. This type of software allows you to write memos, send faxes, prepare reports, develop budgets, play games, and more.

Programming languages are for the real boffins. If you find that the application that you are using to write letters is not suitable you can use a programming language to write a new application.

It is very presumptuous to try and second-guess what will happen with computers in the future. However, some interesting trends are emerging which does give us some idea of what may occur.

Firstly, computers are finding their way into the home sector and this should continue into the future. Already major software manufacturers such as Microsoft are supplying entertainment and educational software for home use.