How and Why Series - 1 - How Does a PC Work? A Simple Overview

When learning about any technology it's important to understand the basics first. It's all too common to rush ahead and tackle complex issues, while ignoring the fundamentals - such as how and why? This article is about using simple metaphor to explain how a PC works in basic terms. It also explains why it is designed that way.

You've seen the outside case - beige, black or some other muted colour, but what's actually inside your computer? Covering all the components would take an age, so let's just cover the basics.

The Processor, RAM, Mother Board and Hard Disk
There are many parts to the computer, but they all in some way support these 4 fundamental parts.

The processor is really concerned with the calculations in the computer. Let's imagine that you've got some accounts to do, with a pen and some paper.

If you scribble sums on the paper, your brain is acting as the processor (CPU - or Central Processing Unit). It's doing the calculating. The pad and pen are acting as the RAM (Random Access Memory). It's where your're storing your results. You'd write them in a format that would enable those results to be fed back in. You might have a total of all your monthly spending and another total of your monthly income. By subtracting your expenditure from your income, you're left with how much cash per month you have left over. Keeping these totals handy for future calculations is what the RAM is for. It's kept very close to the processor, so that calculations and results travel a short distance, very quickly.

The processor and RAM are kept together on the motherboard, for this reason. They are connected by two channels in both directions, the buses, which is how the information travels backwards and forwards (sometimes you will see FSB, or Front Side Bus speed quoted on the specifications - the higher the MHz, the faster the information travels).

The last part of the puzzle concerns the hard disk. If you were working on your monthly accounts, when you'd finished, you'd want to store that information somewhere, such as an accounts ledger; so that you could use it later - say, for your annual accounts. In this respect the hard disk, is like an accounts ledger. It's a way of storing information you use in the short term - for the much longer term. The hard disk has a very important characteristic that the other parts do not share. The processor, RAM and motherboard are volatile. That means that when the power is switched off, the information is lost. So results which need to be kept, are sent to the hard disk, for long term storage.

Why have a Hard Disk? - Why not use more RAM instead?
There is another significant factor to consider here: cost. The processor and RAM are both chips - integrated circuits. The processor is one large one, made of many parts, the RAM is many smaller chips attached to a circuit board. They perform their tasks at phenomenal speeds and hence are costly. 4Gb of memory costs approximately the same as 400Gb of hard disk space, so the reason hard disks exist, is that they offer a lot of space for the money.

So that's it. Certainly there are lots of other parts, that perform many useful and important functions, but they all support this model.

In fact this CPU/RAM design was originally called 'Von Neumann Architecture" and was the basis for all early computer designs. As well as being a formidable mathematician, John Von Neumann was also highly influential in the fields of Computing, Weather Forecasting, Game Theory and Nuclear Physics (working on the Manhattan Project during WW2).

In later articles, we can come back to some of the other parts. To fill in the blanks and flesh out the model, but for now - the processes which occur in a computer follow the same, approximate model a person would use performing calculations with a pen and paper, and storing the results in a ledger.

Copyright (c) Patrick Seery

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Patrick Seery
http://www.ptgr.co.uk

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