You can't afford to miss the bus

When's the best time to buy a computer? According to the adverts and magazines, the answer is a resounding Right Now! This is fairly reasonable since PCs have never been cheaper or more powerful. Of course, tomorrow they'll be even cheaper and more powerful still, but at least you can console yourself having already had 24 hours use out of your machine. With constantly evolving products such as PCs, the best thing to do is to take a deep breath and plunge in - there's little point in waiting once you've decided you want a computer.

Or is there? The more educated buyer will closely follow the roadmap of the single most expensive, and hence influential, component in a PC: the processor. With a little insight into Intel's plans for the next few months, you could make a considerable saving.

Obviously, when the latest, fastest chip is released, all models below get shunted down to lower price points. So if you can put up with last month's state of the art, you could end up with a relative bargain. Just make sure you know when the range is being updated and always buy the second or third chip from the top.

Beyond that, look more deeply than just raw processor speeds. While the advertising glory is grabbed by tarty processors, the real unsung heroes of PC performance are the speed of the memory and external bus. Those in the know leapt for joy when this was recently increased a whopping 50 per cent from 66MHz to 100MHz.

But things are not always what they seem. Long ago, just after the birth of the original Pentium, buyers faced the choice of settling for a dowdy 133MHz chip or splashing out on a brand spanking new - and premium priced - 150MHz. Surely it went without saying that PCs with 150MHz Pentiums would crunch numbers faster than those with 133s - right? Well, not entirely.

While the 150MHz chip was running about 10 per cent faster internally, its memory and external bus were plodding along at 60MHz; compare that to the 133 sprinting 10 per cent faster at 66MHz. These motherboard internal politics pretty much evened up the race between the chips, making PCs built around the cheaper Pentium 133MHz veritable bargains.

So what does the crystal ball predict for the coming months? The Pentium III's debut flavours of 450 and 500MHz are about to be driven down in price by the arrival of a brand new 550MHz model, fresh in the shops as you read this column - all three share an external speed of 100MHz. Come September, we'll be offered a 600MHz processor and an apparently plain 533MHz model. By then, the 550 will be the second most expensive chip in the range, but the two new 533 and 600 chips will boast a faster external bus and memory speed of 133MHz.

Yes, history repeats itself: the relatively average sounding 533 looks set to outperform the more expensive 550 thanks to a 33 per cent faster external bus speed. The smart money this autumn will be spent on the 533MHz Pentium III.

Gordon Laing is a freelance IT journalist.