Overclocking... what are your customers getting into?

by Alan Zisman (c) 1999. First published in Canadian Computer Wholesaler, May 1999

Microcomputers were probably about a week old before the first users discovered that it was sometimes possible to trick the CPU into running faster then the manufacturer intended?overclocking.

While I don?t know of anyone overclocking IBM?s original PC (using an Intel 8088 CPU set to a blazing 4.77 MHz), speeding up the 6 MHz 80286 in the next generation IBM AT was pretty common?at least until IBM hacked the BIOS to refuse to startup at any but the officially designated speed.

In 1990, I bought a 386 CPU and motherboard, second hand?advertised as a 386-25. Sometime later, I discovered that I?d in fact gotten a first-generation 386-16, with the clock crystal replaced to let it run at 24 MHz. (That machine is still up and running at the faster speed?proof that overclocking need not be a destructive process).

Still, overclocking is illegal?at least if it?s done at the retail level, with stores selling, for example, a 300 MHz CPU overclocked to 400 MHz as a real 400 MHz processor.

But while overclocking can void warranties on processors, there?s no law against what a customer does with a product once it leaves the store. And in the last year or so, overclocking has become increasingly popular, at least with some groups of customers.

The boom in overclocking seems to have come about because of a couple of factors:

  • game players  wanting to squeeze as much performance as possible out of their systems, while spending as little as possible.
  • Intel?s original Celeron, which lacked an L2 cache. While this made it a sub-par performer for standard business applications, it made it easy to overclock, often to spectacular levels.
  • A wide price spread between the Celeron and Intel?s official high-performance CPU lines: the Pentium II and now III.

Suddenly, many buyers were getting Celeron-266 systems, and hot-rodding the CPU to speeds close to 400 MHz, resulting in a CPU that performed like a P-II-400 at a fraction of the cost.

With recent steps taken by Intel to limit overclocking, this fad may soon die down. For now, you may not choose to overclock your own system, and you certainly shouldn?t be selling systems running at higher than their rated speeds. But some of your customers are probably planning to hot-rod their systems, and you should know what they?re taking on and what some of the issues are.

Web sites have sprung up filled with information aimed at overclockers. Some of the favorites include:

Firing Squad is claiming over 7 million hits per month?an indication of just how popular overclocking has become.

Overclocking is done by playing with a motherboard?s CPU multiplier and bus speed, in order to send signals to the CPU faster. A stock Celeron 300 CPU in a 66 MHz bus would use a 4.5 multiplier, for example. (4.5*66=297). Leave the multiplier at 4.5 but up the bus speed to 100 MHz, and your CPU is suddenly running at 450 MHz. (You may have problems with your 66 MHz RAM doing that, however). Or leave the bus alone, but up the multiplier to 6.5 and your CPU is running at about 422 MHz, while not stressing out your RAM.

Some tips from the pros:

  • Some motherboards make it easier to do this fiddling. A current favorite is the Abit BX6 series. While other popular boards, like ASUS?s models require changing jumper settings for every clock multiplier or bus speed alteration, the Abit boards let you do it through software?much nicer. As well, while some systems force you to choose either 66 or 100 MHz bus speeds, Abit (and some others) allow a range of speeds in between.
  • Make changes in a series of small steps. Eventually, you?ll hit a threshold, beyond which you?ll start to see system problems?back up a small step.
  • All CPUs are not the same. Even all CPUs of the same model and speed rating are not the same?two seemingly identical Celeron 300s may max out at different speeds, and a few may not allow overclocking at all. A poll on the Sharky site suggests 90% success pushing C-300As to 450 MHz, however.
  • Faster CPUs are tending to be less overclock-able, with reports that Intel is taking steps to make it more difficult to overclock their newest Celeron 433 models. (Sharky Extreme reported disappointment at being unable to push a C-433 past about 488 MHz, after having pushed a C-366 all the way to 550 MHz). Intel is reported to have locked the clock multiplier on recent Celeron models, forcing overclockers to boost the bus speed, which can cause problems for the rest of the system. In fact, there are early reports that Intel has locked the bus speed of its new P-III as well?but given that CPU?s premium price, this step is more aimed at preventing commercial abuse than home overclocking.
  • The biggest problem with overclocking is the potential of overheating the CPU. Firing Squad recommends adding thermal paste (a cheap Radio Shack purchase) between the CPU and the heat sink. Adding fans and heat sinks is highly recommended, especially in extreme overclocking situations. Vancouver consultant, Bill Drake, praises the Global Win fan (Model FAB-24)?a dual fan unit. He points out that it?s like having a backup in case one fan stops working.
  • Be careful upping the CPU voltage (an option with the Abit motherboards). A small adjustment can increase the speed at which a system can boot?but too big a change can fry the CPU. A Celeron can be boosted from 2 volts to 2.1 volts, and maybe to 2.2 volts, but that?s about it.
  • There is the potential of risk in overclocking. 16% of the people responding to a poll on the System Optimization site reported damaging a CPU or computer component.
Once you?ve successfully overclocked a CPU, your system will perform better in some ways, but not necessarily in others.
  • CPU benchmarks will improve, but that doesn?t always mean much in the real world.
  • Business applications, for example, won?t show much if any improvement.
  • Even games may not show as much improvement as hoped for? if Quake is already running at an optimal frame rate, overclocking won?t lead to much visible improvement?but you may notice improvements in situations that would have previously stressed your system
  • 3D rendering and Adobe Photoshop image editing, both of which are pretty CPU intensive, will benefit.


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Alan Zisman is a Vancouver educator, writer, and computer specialist. He can be reached at E-mail Alan