Entry No.60t

IT Writers Awards

[Image P1133 outside.jpg -- caption: The 1133MHz Pentium III test machine is distinguished by the large external fan vent required to cool the high performance chip inside]

[Image P1133 heatsink 1.jpg -- caption: Removing the fan assembly reveals the massive copper slab heatsink on this processor]

Computers have a lot to do with numbers, and one of the numbers that gets bandied about most often is processor speed. Let's look at what processor speed really means, how to make processors go faster -- and, most importantly for the prospective computer buyer, just how much speed you need. We'll also examine the fastest x86 processor currently on the market, Intel's new 1133MHz Pentium III.

There are two main ways to boost performance -- improve the processor's architecture, or increase its clock speed.

The architecture is the design of the chip, including such things as the type of cache memory, which we covered last month, or the number of execution units. Instructions, such as adding two numbers, are carried out by a large number of highly specialised electronic circuits which work together in an execution unit to perform operations on data, which is represented by voltages in these circuits. In olden times, a processor was the same thing as an execution unit, but modern processors have multiple execution units, so they can perform more than one instruction per clock cycle.

Clock cycles are the beats to which your computer marches. The complex electronic signals that make a computer work have to be kept in step with each other, and this is achieved by having a central clock which tells all the components when to perform the next step in their task. The faster the clock, the faster the processor will perform -- but if you make the clock too fast, the circuits will overheat or get out of step with each other. Clock speeds on current processors are measured in Megahertz (MHz), or millions of cycles per second. An 800MHz processor "ticks over" 800,000,000 times every second, and may perform more than one instruction during each of those ticks.

Pushing the envelope
Changing the basic design of a processor is a very complex and expensive task, so during the lifetime of each basic processor design, most of the performance improvement is gained by making the same designs go faster. With each increase in clock speed come problems that have to be solved, and most of those problems revolve around heat.

A chip running at a higher speed also tends to need a higher voltage, which exacerbates the problem by generating still more heat. While an 800MHz Pentium III uses 1.65 or 1.70 volts and produces a nominal 21 watts of heat, a 1000MHz chip requires 1.70 volts and produces 26 watts, while pushing the clock speed just 133MHz higher to 1133MHz means boosting the voltage to 1.80V and increasing the heat to 35.5 watts. That's a 36% increase in heat, for a 13% increase in speed. Because chips are easily damaged by heat, this is a big problem.

Our test unit was a pre-production 1133MHz Pentium III supplied by Intel, with its own test machine. The chip was equipped with a handmade copper heatsink, seen in the picture, and mounted on a specially modified motherboard. Most heatsinks are made from aluminium, but copper is a better (and more expensive) conductor of heat.

Intel takes the cooling of this chip quite seriously, since the base of the heatsink is a solid 6mm thick copper slab that's about 10cm long and 5cm high. The hand-soldered copper vanes on this heatsink are served by a large fan which draws air out through a special vent on the side of the machine. Production versions are less extreme and will run in standard cases and on some standard motherboards -- those that have enough room to fit the more conventional twin-fan heatsink mounted on them.

To see the kind of performance of which this system was capable, I replaced the video card with the latest GeForce 2 high speed model, and tried a few benchmarks. As might be expected, results were spectacular, with game performance of 7058 3DMarks and a general performance score of 198 Sysmarks. This compares to the fastest computer in this month's Best Buys section, a 1000MHz Athlon, which managed 4271 3DMarks and 177 Sysmarks. There's no doubt that the Pentium III at 1133MHz is the fastest chip we've ever seen at PC World, but the computer industry being what it is, there will be an even faster one any day now.

Conclusions
Cutting edge high speed computers are like performance marques -- the Lamborghinis and Ferraris of the PC world. They can give you a feeling of prestige during the few months, or weeks, that they are at the top of the heap, and if that's worth paying twice the money for bleeding-edge technology, then that's fine for you. It's useful to look at these machines, though, because the new and expensive technology of today will be commonplace and cheap in a couple of years.

Most people who want a computer will look for a compromise between speed and power that best suits their needs. For run-of the-mill office work, a Celeron or Duron of around 600MHz would be adequate, and much cheaper than high performance alternatives. An expensive 3D accelerator card is unnecessary in a system that won't be playing games or movies, so you can save a few hundred dollars by using a basic video card, or a motherboard with built-in video.

A multimedia computer used for games and the like can't be too fast, but in practice, I find aiming for one that's about 20% behind the very fastest gives a good balance between speed and cost. At present, Athlons and Pentium IIIs of 800MHz and above, when equipped with a high performance video card such as a GeForce, are capable of dealing happily with just about any software that's out there today.

Getting a processor that's at the top of the speed range usually costs more than twice as much as one that's in the middle of the range. In terms of real-world performance, investing that money in a faster video card, better motherboard and more memory is probably a better bet for the average buyer. But if you're fanatical enough to spend big for the very best, there's a lot of interesting technology out there.

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