How PCs Work

Posted on 27 Jan 2005 at 16:28

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Bamboozled by binary? Don't know the difference between your hard disk and your RAM? Then step right this way. MARTIN COOPER lifts the lid on what happens behind the scenes in your PC to explain what each component does - and what to look for when you are buying them.

So how does your computer work? It sounds like one of those impossible-to-answer questions, such as: "What is the meaning of life?" or "when did the universe begin?" Maybe one day, someone will be able to find the answers to those. Today, we are going to lift the lid on the inner workings of your PC. It is a far simpler conundrum.

If you didn't enjoy physics and maths at school, and suddenly feel your blood running cold at the thought of complex formulas and obscure electronic principles, do not worry. We didn't like them much either - so you will not find any obscure and mind-bending physics here. Instead, we will employ plain English and common sense as we explore what is going inside your PC.

Of course, you might be asking yourself: "Why should I worry about how my PC works?" You put petrol in your car and seldom think about why it starts. Why start worrying about what makes your PC tick? Well, there are distinct advantages to understanding how and why your computer works. The main one being, if your PC goes wrong you will be able to work out why it is misbehaving. Armed with this information, fixing it should be much easier - and you will not have to pay an expert to come to your house and mend your machine.

Ones and Noughts

At the most elementary level, computers work like a huge collection of switches. By flicking these on and off in different orders, they can create numbers and then perform mathematical calculations using them. By adding more switches, you can work with bigger numbers at a time, and carry out more complex mathematics. Flick the switches faster, and the maths can be done more quickly. The switches inside your PC are microscopically small transistors. Pentium 4 chips, for instance, contain about 155 million of them.

So how does turning switches on and off enable the PC to calculate numbers? The answer is that PCs count using base two or 'binary'. Ordinary maths uses the decimal system, where the last digit of a number represents zero to nine, then the next digit along represents tens, and the next hundreds. Binary only counts up to two before carrying a figure over to the next column - so one is 1 in binary, two is 10, three is 11 and four is 100. This means that you only need two different digits to create any number - 0 and 1 - and you can represent these using switches that are on (1) or off (0).

As we will see there are other ways aside from switches in which these numbers can be stored - magnetic north and south poles, or bumps and flat areas on the surface of disks. To learn more about how binary works, check out the table below. It might look a little daunting, but, we promise, it is not as difficult as it appears.

Switching your PC on

Unlike us, when a computer is switched on in the morning it has absolutely no idea what it is, what is going on or what it is going to do. Okay, so maybe that describes some of us the moment the alarm goes off on a Monday morning. But soon enough, your brain remembers you have two arms, two legs, eyes, ears, a nose and a mouth. A few moments more, and you are pretty happy to get up and get going.

To get up and running, your PC begins its wake up, or 'boot up', process by running a small program that seeks out what is inside the machine. It looks for core components, such as the processor, hard disk and memory, and then lists other items, such as sound and graphics cards, as well as other essential components. When it finds them it records their name or model number, and some essential details about them.