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If you can't stand the heat...

Guy Kewney AnchorDesk

Published: 24 Mar 2000 17:14 GMT

The question was a trick question. I already knew that if we ran the PC Mag 3D Winbench test on his biggest, fastest machine, it would start out with truly astonishing frame rates, but that if you kept running the test, it would slow down to a crawl. What I didn't know, was whether this guy knew it.

His response was calm and measured: "Of course it's not true!"

He explained that the processor was a Pentium III, not even slightly over-clocked. I agreed with him; he was right. The processor wasn't slowing down. It was the 3D accelerator that was doing it.

"Oh, no, I don't think that's possible," he said.

Either he's a particularly clever and convincing liar, or he's just one of a dozen or so PC makers I contacted who genuinely don't know that they are shipping a dog. I know this chap; I'm convinced he's not lying. I think he doesn't yet know what is creeping up on him.

The problem lies, not in the processor, but in the chips - bigger than a Pentium - which power the breakthrough Nvidia GeForce graphics cards. Most of the time, these chips sit pretty idle in the box of your PC. But what they are supposed to be good at, is drawing triangles. And they are - frantically fast. Throw a request for a triangle-drawing operation, and they'll send your images straight to the display. Get more enthusiastic, and send more, and they'll handle them, too. But there comes a point where you will find that you are overloading them.

What happens then, it seems, is that they start using all the transistors on the graphics chip, and these all start switching furiously, and the temperature goes up. And even though the graphics cards are actually fitted with cooling fans - two of them per card, in some cases - to pump this heat away, they simply aren't efficient enough to cope with a full load of triangle calls.

The chip responds by slowing itself down. It is designed to do this, although this feature of the design isn't, perhaps, widely advertised.

So who has noticed?