The world of PCs is rife with arcane terminology and much of it harks back to earlier times, when you needed to know your bytes from your boot partitions if you were to get the most from your beige box of tricks.

Thankfully those days are almost behind us, but there are still some parts of a PC that you'd do well to know a bit more about.

Chief among these is the BIOS (pronounced 'bye oss'). Short for Basic Input Output System, this is a program built into PCs that runs automatically as soon as the PC is switched on.

The BIOS controls the very basic functions of a computer and is responsible for such things as checking that the processor and memory are present and working, and looking for a disk drive to boot from.

The BIOS also handles the basic configuration of other components too, such as sound, graphics cards and various ports. The operating system may take care of making these components actually work but without the BIOS, it wouldn't get very far.

Under normal circumstances, the BIOS goes about its business without drawing any attention to itself, apart from perhaps displaying the odd message on your monitor when you first turn your PC on.

There are times, however, when you will need to delve into its recesses, such as when you fit a new hard disk or processor, or even upgrade your operating system.

Most PCs come with a manual that claims to explain the BIOS but these usually gloss over even the most basic of details. What you really need is a plain English guide that tells you everything you need to know. Just like this one, in fact!

BIOS basics
The BIOS is stored on a chip on the PC's motherboard. There are countless different makes of motherboard but only two companies actually produce BIOS chips - Award and AMI.

Each manufacturer's BIOSs look a bit different, as do BIOSs on different PCs, but the BIOS screen layouts and options are fairly standard and once you're familiar with one, you should be able to figure out another.

So, first things first: how do you get to the BIOS? Most computers will show the key on the keyboard you need to press when the computer is first turned on. It is usually F1, F10, F11, F12 or the Delete (Del) key - look for an on-screen message along the lines of "Press F1 to enter Setup".

Some computers will only let you enter the BIOS when the PC is first turned on and not after a reset. Sometimes you just have to guess and try tapping the different keys when the computer starts to find out.

The first thing to remember when entering the BIOS is not to change any setting that you don't understand. Some options can stop your computer from working properly, or at all, and some can even stop you from getting into the BIOS again to change them back.

If you decide to change several options, it's a good idea to change one at a time and restart your computer after each one. That way, if one of the changes causes problems, you'll know what it was and can easily change it back.

Getting around
Almost all BIOSs are organised into a series of 'screens', with each being accessed from a menu running across the top. Enter one screen and there may be further options that take you into sub-screens. Pressing the Escape (Esc) key will return you to the previous one.

The first screen you'll probably see when entering the BIOS will show the date, time, a few other useful bits of information and instructions for navigating between the screens and making changes.

For example, on our computer, options you can change are yellow and surrounded by square brackets. Text that is coloured grey is information and cannot be selected. You can change settings by pressing the + and - keys or you can press the Enter key to display a list of options.

The other two important options in the main screen are 'Exit Without Saving' and 'Save & Exit Setup'. They are self-explanatory but it is worth emphasising that if you have changed something and are in any doubt about whether it will damage your computer, select Exit Without Saving and then try again.

Why change BIOS settings?
Fitting new hardware can sometimes mean you have to edit the BIOS. Most computers will find any new hardware automatically but sometimes you need to tell the computer where it is.

The most common task is fitting a new hard disk. The BIOS can detect new drives automatically but as this increases the boot time, this feature is often disabled by default. In this case, the new drive won't be detected when the computer starts.

To change this, enter the BIOS in the usual way and select the Standard CMOS Features option. Here you will see a list of the drives connected to your computer as IDE Primary Master and Slave, and IDE Secondary Master and Slave.

Move the cursor down to where it says (None) and press return. Select the Auto option and your hard drive should be detected automatically.

Get your boots in order
A very useful setting the BIOS allows you to change is how your computer boots. When it first starts, the BIOS looks for a disk containing an operating system to boot from.

Usually, this is the hard disk but there may be times when you want to boot from a floppy disk or a CD-Rom. Which drives are checked and in what order is determined by the Boot Order in the BIOS.

Changing the Boot Order can make your computer more secure as it gives you more control over how it starts. Even if Windows is password-protected, it is possible for someone to start the computer with a floppy disk or a CD.

Alternatively, if you want to stop someone messing around with your computer, you can do so by restricting how the computer starts and make your computer look on your hard drive for an operating system first.

Enter your BIOS in the usual way and enter the Advanced BIOS Features screen. You will either see a list of the devices the BIOS checks, or an option to change the boot order.

To make our computer more secure we are going to change the first boot device to HDD-0, which is short for Hard Disk Drive 0, or the first hard disk, in other words. Move down to First Boot Device and press Enter to see a list of devices the computer can boot from. Move down to HDD-0 and press Enter again.

Changing the boot order for troubleshooting is effectively the reverse of this process. There are lots of very good troubleshooting tools that you can load from CD or floppy disk. If there are problems with the hard drive, you may need to make the computer look elsewhere first.

This might be necessary if Windows has a fault that stops it from loading properly or if you want to boot from the Windows CD-Rom in order to reinstall it. Return to the Advanced BIOS Features screen and change the First Boot Device to the media that you want to boot from.