Computers: Swapping new PCs for old: William Gallagher tears out his innards and enhances the performance of his system

YOU WAS robbed. When you paid pounds 3,000 for that state-of-the-art 386 PC- compatible system four years ago, you may well have got a good deal. Probably no one tried to con you. Perhaps you even got a good working life out of it. But try to run the latest version of Microsoft Word or Wordperfect on your 386 PC and it laughs.

There are two reasons for this, a simple one and a trickier, more detailed excuse. The simple reason is that many of us bought PCs based on 386 processor chips and the industry would like us to buy the latest - and more expensive - PCs based on 486 or Pentium chips.

Alternatively, look at it this way. The latest software is rich in all kinds of useful features: just compare a new spreadsheet program Lotus Improv or Excel version 5 to the pioneering Visicalc. Using the latest software, you can juggle multiple spreadsheets in your office, keep every chapter of your novel open at the same time and give office photographs a cruel twist with image manipulation packages.

But the cost of all this is the power required to run it; and while there is a lot to making a PC work faster, the crucial part is the processor. And a 386 processor cannot cut it any more.

So you may well want to throw it out and get a latest-generation 486-processor system. You do not, though, have to throw out your whole PC and replace it. Instead for between about pounds 170 and pounds 400 you can swap out the innards for faster versions and, with some planning, have yourself a true 486 PC. What you need to swap is the motherboard: the main circuit board that the processor sits on.

Changing the processor chip alone is not enough to speed up your PC. That is because while the processor does all the calculations to handle your budget spreadsheet, it is the screen and the video circuits that display the 3D charts and it is the motherboard that processes the signals from one to the other. You need to swap the lot to get a real benefit.

Half a dozen companies such as Watford Electronics and Simply Computers will sell you a new 486 motherboard, but you have to make some further choices. While processors have improved, most of the rest of the PC has developed, too.

Most monitors require a special circuit board to connect them to the rest of the machine, known as an expansion card and these cards are what have changed most over the last few years.

When you got your 386 these expansion cards were all of one type. They were so common that they did not have a name. Now they are referred to as ISA cards - Industry Standard Architecture - to differentiate them from the newer 'local bus' and PCI, 'peripheral component interconnect' cards. These are different ways of doing the same thing. Instead of the signals from the processor having to go halfway round the motherboard to get to your monitor card, they get there more directly. More directly means faster and with Windows, the PC's graphics-based operating system, pumping out dialog box after display screen all the time, faster is required.

Your old expansion cards will not fit PCI or local bus slots. All of the motherboards you can buy now will have some of these new slots. So it is a question of finding out how many cards you have and how many slots on the new motherboard are ISA ones which will fit your old cards. The best situation is where you have only a couple of cards and they fit. The worst is where you will have to buy a new card or two. In practice, you will normally find that upgrading the motherboard is sufficient.

However, you may prefer to buy new expansion cards. If you are upgrading specifically to run Windows at anything approaching a decent speed, you will need a PCI or local bus graphics card. These relieve the main processor of the donkey work of calculating screen displays and let your 486 get on with other things. There are a dozen graphics cards from different companies, but look for ones that are based on Cirrus logic chipsets. These will cost you less than pounds 70.

Odds are, though, that the motherboard will not come with enough main memory (ram). You must have 4 megabytes of ram or you will spend as much time waiting for your 486 to do something as you did for your 386. Some common word processors such as WordPerfect 6.0 for Windows or Word 6.0 may need at least 6 megabytes.

If you can, budget for 8 megabytes - you will get some with the motherboard, otherwise it costs about pounds 30 per megabyte. It is easiest to buy ram from the same company that sold you the motherboard, but watch for wildly different prices from different vendors.

Look out, too, for the speed of the ram. If your ram cannot switch data about quickly, the extra speed of the processor chip will be wasted. Tell the firm from which you are buying ram what you want it for and tell them exactly what motherboard you have bought.

You can also expect to have to replace your hard disk, for similar reasons. Slow transfers to and from hard disks can be can severely impede performance. You should not buy a hard disk with less than a 100 megabytes of storage capacity. Disks of 250 megabytes are now common and cost about pounds 170. Today's IDE - 'integrated drive electronics' - disks are much faster than most 386 hard disks .

Macintosh users have long been familiar with the idea of upgrading machines and have become used to the sight of Apple ripping off everything but a strip of plastic at the back of their Mac, replacing it all and calling it a minor upgrade. The difference with Apple is that the company keeps the old motherboard. You, though, can look forward to many happy hours with your old 386 PC motherboard and can even hang it on a wall - not as uncommon as you might think.