Overrclocking your CPU can improve system performance. But be careful: indiscriminate overclocking can damage your CPU.

Overclocking means pushing a processor’s clock speed beyond its standard speed. For instance, taking a 100 MHz Pentium and running it at 120 MHz. Just about any chip can be overclocked by about 15 percent, or even 20 percent with very good cooling. This is not bad for a CPU, as long as you don’t overdo it and you provide adequate cooling.

The CPU’s clock speed is the system bus speed multiplied by the bus speed multiplier. The bus speed multiplier defines the CPU’s raw speed. For example, a K6-200 and a K6-300 both have the same bus speed of 66 MHz, but different bus speed multipliers of 3 and 4.5. So the K6-200 has a clock speed of 66 MHz x 3 = 198 MHz. And the K6-300’s clock speed is 66 MHz x 4.5 = 298 MHz.

You can overclock your CPU in one of two ways: by increasing the CPU’s bus speed multiplier, or by increasing the bus speed. 

Increasing the multiplier

When we overclock a CPU working at 66 x 3 = 198 MHz to 66 x 3.5 = 231 MHz, we increase the CPU’s clock speed and not the bus speed. You gain 15 to 20 percent in performance with such overclocking. Don’t overclock by adding more than 0.5 to the bus multiplier, to prevent system CPU or system damage.

Increasing the bus speed

This method requires your motherboard to support multiple bus speeds. Older motherboards don’t have this option. Most new motherboards support a 75 MHz system bus, and many support a 83 MHz bus.

When we overclock a CPU working at 66 x 3 = 198 MHz to 75 x 3 = 225 MHz, we’re pushing system bus speed from 66 to 75 MHz. And letting RAM, external cache, video card, and the hard drive talk faster to the CPU, improving performance 25 to 33 percent.

Thus you can try different bus speeds and bus speed multiplier combinations. You’ll find that a system with a higher bus speed performs better. So, a CPU running at 75 x 3 = 225 MHz performs better than a CPU running at 66 x 3.5 = 231MHz. Even though 231 MHz is greater than 225 MHz.

Again: never increase the total system speed (bus speed x bus speed multiplier) by more than 33 to 40 MHz.

When companies like Intel or AMD make a CPU and claim that it can run at 233 MHz, it means that it is guaranteed to work at 233 MHz even in the worst possible environments. Now, if you make the environment better, you’ll be able to squeeze some extra performance (up to 266 MHz in this case) out of it. Heat is the CPU’s number one enemy, so if you can keep the chip cool, you can run it at a speed higher than rated.
 
 

Before overclocking a Socket 7 CPU (Cyrix, Intel, and AMD), make sure you have all these things:

Your motherboard manuals

A good fan and heatsink

Heatsink paste or silicon grease

Here’s a ready reckoner for some common CPUs (see table above).

Be sure that your processor is genuine and not a "re-stamped" one—which has been stamped with a higher speed than it was designed for, to start with.

The success of overclocking depends a lot on the type of motherboard used. The motherboard market is flooded with cheap imitations, so make sure you have the genuine item.

Your motherboard should support as many bus speeds as possible—66 MHz, 75 MHz, and in some cases even 83 MHz and 100 MHz) and should carry a warranty.

In some cases, you can "flash update" your motherboard with BIOS updates to let it take later CPUs.

Read your motherboard’s manual carefully and locate the CPU frequency and voltage setting jumpers. First, make sure that the settings are proper for the actual speed and core voltage of your CPU. All this data is generally given at the bottom of the CPU, and is also mentioned on almost all motherboard manuals. CPUs have two voltages, the VI/O input output voltage and the VCORE core voltage. Most current processors have a fixed VI/O at 3.5 V. The core voltage varies from 2 to 3.5 V. Make sure you have the correct core voltage setting for your CPU.

Now fit the CPU in the ZIF socket, and attach the power and other cables to the motherboard, and switch on your system. Enter the system BIOS by pressing delete at startup and reset the BIOS settings to default—by selecting "load BIOS defaults" from the main menu in the BIOS.

Unplug your PC’s power cord and consult the motherboard manual for any CPU frequency jumper settings that fall within 33 MHz of the actual speed of your CPU. For example, if your CPU is a K6 PR233, then find the jumper settings for a K6 PR266 and set the jumpers accordingly. You’ll have your system overclocked to 266 MHz. Motherboard manuals typically provide tables of jumper settings for various CPUs. Don’t tinker with the CPU voltage settings, and keep the system’s cover open as it helps in faster dissipation of heat.

After you have finished setting up the jumpers, recheck to make sure you’ve selected the right combination and the right speed. Now attach the fan/heatsink combination and proceed as given below.

Reconnect power and boot up. Use the PC for some time and try to run CPU-intensive apps such as heavy graphics.

If the system works fine, then give yourself a pat on your back: you’ve successfully overclocked your CPU. If the system hangs frequently, or displays abnormal errors (memory and display) then you’ve probably selected too high a setting. Turn off the system immediately.

If the chip is too hot, try using heat-sink compound (available at any good electronic equipment shop) to improve heat transfer between the chip and the heat sink. Put on the machine and use it for some time. After ensuring proper cooling of CPU, you can close your system.

Overclocking PII class CPUs

I’ve tested four motherboards—EX98 (Azza), BX98 (Tomato), 440LX (Intel), and an Abit BX6, which I ordered online. The BX6 is a good board for overclocking. It supports every bus speed possible and has great hardware monitoring and security features, you can even change the voltage settings, but the BIOS is very different from the other three. But the BX6 may be difficult to come across, so we’re not discussing it here.

Almost all the motherboards made for PII or Celeron processors are equipped with Award BIOSes. This BIOS has a menu for CPU configuration. Just select a bus speed one step higher than your CPU, or select a CPU speed 33 MHz greater than that of your CPU. Things should work just fine. The Celeron 300A is overclockable to 100 MHz bus speed, if you have a motherboard that supports bus speeds of 100 MHz). So you can overclock it to 100 x 3.5 = 350 MHz—where it performs better than a PII/350! Remember that you’ll need a really great cooling fan for the CPU. Maybe a 220V 6" cooling fan in a well-ventilated cabinet…mine runs without a cabinet!