A computer performs two main operations. It processes data and it stores data.

As far as the processing is concerned a computer is similar to a hand held calculator. With a calculator you type in some numbers and press the equal sign to see the answer. All of the work is done in a processing chip. So too with the computer.

The computer contains a central processing unit, which is located on the main computer chip. This central processing unit receives data and processes it ready for display on the screen or a printer.

The processing chip is usually the one that is used to measure the power of the computer. These chips are usually described by a series of numbers 8088, 80286 (or 286 as it is known), 80386, 80486, 80586 (or Pentium as it is more commonly called). The higher the number the more powerful the processor. Power in this context meaning the ability to handle processing instructions in a given time.

Where the computer differs from the simple calculator however is in its ability to store data. The computer is capable of handling large amounts of data. Since the data cannot all be processed at the one time the data is stored temporarily in a series of computer chips known as the random access (RAM).

The best way to think of RAM is like pigeonholes in a post office or a mailroom. Data comes in from a variety of sources (keyboards, disks, modems, whatever) and is placed into a pigeonhole in RAM waiting its turn through the processor. Once processed the data is again placed into the pigeonhole waiting for dispatch to an output device such as a printer or a monitor.

So RAM is a temporary area of storage used to hold data waiting processing or dispatch to other devices. The important thing to remember about RAM is that it is actually just a series (or bank) of computer chips and is available only when the computer has power.

The use of RAM presents two problems.

Firstly, if the power to your computer fails even for a brief millisecond all the data in RAM will be lost.

Secondly the size of the RAM is finite. It can only be as large as the installed chips can hold - at some point RAM will be filled and some of the data in there will need to be placed elsewhere.

It is for these reasons that computers allow you to save data to more permanent forms of storage such as floppy disks and hard disks. Floppy disks and hard disks are like RAM in the sense that they hold your data, but are unlike RAM in the sense that they store data in a more permanent form that is retained even when the power is switched off.

RAM and the amount of disk storage in the computer are often used to refer to the computer’s capacity. For example, you will hear people talk about a computer with 16 megabytes of RAM and 500 megabytes of hard disk space. Again, the higher the number the greater the capacity, and therefore the more desirable the computer.

The capacity of both RAM and disk storage is measured in bytes - each byte is roughly equivalent to an alphabetical character. For example, to store the name MARY in a computer would require 4 bytes of storage.

However, since storage is so immense its capacity gets measure in kilobytes and more often than not in megabytes.

If you drive a car you will know (hopefully!) that 1-kilometer is made up of 1,000 meters. If you do some cooking or lift weights you will know that 1 kilogram is made up of 1,000 grams.

Therefore 1 kilobyte must be equal to 1,000 bytes, right! Wrong! Because of a mathematical extrapolation 1 kilobyte is actually made up of 1,024 bytes - but who’s counting in computers? For most of us 1 kilobyte is roughly equivalent to 1,000 bytes, and 1 megabyte is roughly equivalent to 1,000,000 bytes.

To give you an idea of how computing capacity needs have changed over the years, the original IBM computer had 64 KB (that is kilobytes) of RAM. Today most computers have 16 MB of RAM standard so that they can run modern programs.

Every computer needs software (computer instructions) to make it come alive and work.

When you first switch on your computer two vital pieces of software are used.

Firstly the computer performs a test of itself to ensure that its main components are working satisfactorily. This test is called the Power On Self Test and the software has been etched into a special ROM (Read Only Memory) chip. (Your programmable microwave, or washing machine, or video, or whatever, also has these types of chips that contain operating instructions for the machine).

The second piece of software is the operating system which contains instructions telling the computer how to interact with the various devices such as monitors, keyboards, disk drives, printers, and the like that are connected to it.

The most popular operating system used by personal computers is the Disk Operating System (or DOS) which is written by Microsoft - remember, Bill Gates!

Now the real rub comes with the fact that the operating system can be tailored so that the computer automatically loads other programs for you. This usually consists of software for checking viruses, or displaying a menu, or changing the way that the screen looks using something like Microsoft Windows. Because the start-up of computers can be infinitely customized it is not possible to give you one single set of instructions here to tell you how your computer will start - every computer will start up in the way customized by its owner.

So when you flick the switch the computer will burst forth with a flurry of activity. Some will then leave you with a blank DOS screen, many will display a special menu of choices, and others will start with Microsoft Windows.