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How you can 'overclock' your PC and why you may not want to

June 9, 1998
Web posted at: 5:00 p.m. EDT

by Brad Grimes

PROBLEM: You want to speed up your PC for free but don't know if forcing it to go faster is a good idea.

SOLUTION: Learn what you'll be doing to your PC, and if you decide to go for it, do it right.

Last March, Karl Zimmerman bought a new PC--but it wasn't the PC he really wanted. Like many of us, Zimmerman was on a budget and needed to compromise.

"I had to make some trade-offs in putting together my system," says Zimmerman, a software engineer at a Silicon Valley medical company. "One trade-off was to select a lesser CPU than I wanted and apply the money saved to upgrading other components."

In the end, Zimmerman bought a Pentium II-266 system with 64MB of RAM. That's a pretty fast chunk of hardware, but Zimmerman wanted more. He'd learned about overclocking the way many people do--from an Internet newsgroup. Simply put, overclocking means changing some of your system's settings to make it run faster than it was designed to go. Following an online trail, Zimmerman read about his PC's motherboard and decided he'd try to overclock it. The result? "My system is now ticking along at 300 MHz," he reports.

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Sounds great: You pay for one PC and end up with something faster. But Zimmerman's success doesn't mean overclocking is as natural as slipping your car into high gear. Check the newsgroup comp.sys.ibm.pc.hardware.chips, and you'll see as many "my PC is screwed up" postings as you will "my PC is reborn." Because overclocking sounds so easy, people don't bother to learn about the risks. And there are plenty, from overheating to voiding your warranty.

Overclocking 101

This minicourse is like Sex Education 101. We're not saying do not overclock your PC, though we strongly advise you not to. But someday someone is going to tell you how wonderful overclocking is, so you need to protect yourself and avoid taking unnecessary risks.

The speed of your PC is determined by the speed of the system bus and by something called a CPU multiplier. Change one or both and you have a faster PC. Zimmerman's original PC had a multiplier of 4 and a system bus speed of 66 MHz. He changed a jumper on his motherboard to accelerate the bus to 75 MHz, which boosted the system to 300 MHz (75 MHz multiplied by 4).

Simple enough? Not really. After he first jumped his system bus, Zimmerman says, his PC still wasn't functioning at top speed. He posted a message at a newsgroup and learned he needed to adjust his PC's CMOS. Finally, the system ran just right.

But just because overclocking worked for him doesn't mean it will work for you. For one thing, not all motherboards support speeds over 66 MHz. And some component manufacturers are taking steps to discourage overclocking. Intel has started to design its CPU multipliers so they can't be changed.

Even having a system that can be overclocked is no guarantee of success. Charles Kozierok, MIS director at a Massachusetts manufacturing firm and Webmaster for The PC Guide (www.pcguide.com), cautions that what seems like a good arrangement initially can turn disastrous down the road. On The PC Guide site, Kozierok warns would-be overclockers that "whether you succeed or not [in overclocking] is as much a matter of luck as it is of skill."

For one thing, a PC running faster than intended may overheat and crash. Other dangers include shortening your CPU's life span and damaging other system components. What you end up with is general instability. Once you've overclocked, if a software program starts locking up, you can't be sure of the cause.

Kozierok says that inexperienced PC users should refrain from overclocking unless they have a spare PC they'd like to tinker with. Ultimately, the benefits may not be worth the trouble. According to our PC WorldBench tests, the average Pentium II-300 is only about 6 percent faster than the average Pentium II-266, an increase you're unlikely to notice in the programs you use most.

Wasted Cycles

Still, some people say overclocking is a good, natural thing. In fact, it has been around since the old days when people were replacing 6-MHz clock crystals with 8-MHz crystals in their 286-based PCs.

Scott Wainner, Webmaster of System Optimization ( www.sysopt.com) is an overclocking advocate. While he advises people to be careful, he says that anyone who does CPU-intensive tasks is wasting CPU cycles by abstaining.

If you decide you want to overclock your PC, we offer the following guidelines:

• GET THE WHOLE PICTURE. Hit the Net and read all you can about overclocking.

• READ YOUR MANUALS. Make sure your PC can run at faster speeds. You'll probably have to call your motherboard manufacturer to find out for sure.

• COOL IT. Buy a bigger heat sink and even a CPU fan. Overheating is probably the biggest hazard, so be prepared.

• BACK UP YOUR HARD DRIVE. You'd do this before performing a normal upgrade, so you should definitely back up before doing something your PC never expected.

• TEAR UP YOUR WARRANTIES. You might as well save some shelf space, because your warranties will be void if you start fooling around with the system's bus speed.

• BE REALISTIC. If you must try overclocking, don't go too fast. Start with small speed boosts, like 266 MHz to 300 MHz. Remember, pushing a PC too far is a recipe for disaster.

• DON'T BE AFRAID TO CHICKEN OUT. If you overclock your system and something isn't right (you get a boot error, the system locks up, programs crash), change it back at once. But be forewarned: Sometimes you can't undo an overclocking mishap.

Brad Grimes is a senior associate editor for PC World.