Q I have heard a lot about computer viruses but I don't really understand what they are. Can you explain?

A A computer virus, despite its sinister name, is simply another computer programme designed to make copies of itself, usually through some medium where it can be spread to another computer (email, floppy disk, etc.). Each copy also makes copies of itself and so on. In this way, these programmes can spread incred-ibly quickly, especially if spread through email attachments, such as the recent Love bug email virus. After a certain number of generations, the virus usually becomes more active and will carry out some action. Depending on the vindictiveness of the virus author. you can be presented with an annoying message or, more seriously, a corrupt hard disk.

Q I want to upgrade my PC by changing the motherboard from a Pentium 200mhz to a Pentium III 900Mhz. Do you have any advice?

A The problem you will have here is the standard Pentium case will not take a new Pentium III board because newer motherboards require something called an ATX compliant case. You will need to buy a new case. You can pick one up for around £40 (www. scan.co.uk) but it is also likely that you will have to change the meory to fast 168 pin DIMMS. For a good online guide on how to proceed, go to: www.zdnet.com/ pcmag/pctech/content/16/13/_open.htm Q How much RAM should I have in my computer for it to work best?

AIt depends on what operat-ing system you have and what you are using your computer for. Windows 98 will run happily with 32mb but will work best with 64mb or above (although above 64mb the benefits are not as dramatic). Windows NT (including Windows 2000) needs at least 64mb and really needs 128mb to work best. The memory management on NT is much better than Windows 98 and so the more memory you have the better. If you are manipulating very large image files, you should fit as much memory as possible as this will help prevent Swapping, which occurs when the operating system runs out of RAM and starts using the hard disk instead (which is approx 1,000 times slower than RAM).