There are two traditional ways of overclocking your CPU – i.e. to configure it to use a higher clock rate. One is increasing the CPU base clock (or the CPU external clock). The other is increasing the CPU clock multiplier.

The clock multiplier is usually locked, meaning that you cannot increase it. This “feature” is called “overclocking protection” and was introduced to prevent people from counterfeiting processors (in the past people erased the original CPU markings and wrote something else, selling it as a higher-clocked CPU). Today only Athlon 64 FX processors have their clock multiplier unlocked, so this overclocking technique is an option with these CPUs. Athlon 64 CPUs, however, can be configured with a lower clock multiplier. Combining a lower clock multiplier with a higher base clock is a very effective overclocking technique and we will talk more about this later.

The most popular overclocking technique is increasing the CPU base clock or the CPU external clock. But since all system clocks are linked together, when you increase the CPU base clock, you actually increase all clocks used in your PC. So you may find yourself limited by a device other than your CPU.

Let’s give you a real example (for now consider that your motherboard doesn’t have any fancy overclocking option as we will talk more about them later). Consider an Athlon 64 3800+ using DDR400 memories. This CPU runs originally at 2,400 MHz, uses a 12x clock multiplier and a /12 memory divider.

What will happen if we increase its base clock to 225 MHz? Well, the CPU will run internally at 2,700 MHz, a 12.50% increase on its internal clock.

But the side effect is that your memory will be running at 225 MHz (450 MHz DDR), the HyperTransport bus will be running at 1,125 MHz, PCI Express busses will be running at 112.50 MHz, Serial ATA ports will be also running at 112.50 MHz, AGP bus (if your motherboard is an old one) will be running at 75 MHz and PCI bus will be running at 37.5 MHz.

Everything on your system will be overclocked. At first this seems great: a better performance, you think. But if you are unable to increase the CPU base clock up a certain level, you won’t know which device is preventing you from overclocking your system even more. Is it the memory? Is it the video card? Is it the motherboard chipset? Is it the Serial ATA hard disk drive? Is it an add-on card?

That’s why high-end motherboards targeted to overclocking allow you to configure the clock rate for each individual device. This configuration can be a simple lock (i.e. locking the device clock to its default value), can be a full-configurable clock option or can be a multiplier or divider configuration.

If your motherboard has such configurations, we recommend you to use them, and only try to overclock other devices like the PCI Express bus (i.e. your video card bus) after you found the highest base clock supported by your system. Let’s show you how.