Increasing the CPU speed

Before we do this, you need to understand how the CPU speed is calculated. It is calculated using a multiplier and the bus speed. The multiplier is just that, a number used to multiply the bus speed. The bus speed is a little more complicated. Depending on your motherboard, there are several bus speeds available. Standard bus speeds are 66 and 100 (in newer systems). The bus speed determines how fast the CPU can transfer information to other devices. There are several busses. The front side bus is how the CPU sends info to the memory. The PCI bus is how information is transferred to your PCI devices, such as sound card, modem, etc. and depends on the front side bus speed. The AGP bus is a newer type of video slot and has its own bus speed.

In a 66 MHz system, the front side bus runs at 66 MHz, the PCI bus at half that, 66 / 2 = 33, and the AGP bus at the same speed as the front side bus, 66 MHz.

In a 100 MHz system, the front side bus runs at 100 MHz, the PCI bus runs at a third, 100 / 3 = 33, and the AGP bus runs at two thirds, 100 x 2/3 = 66.

It is very important that you remember this, because if you increase the front side bus, it will effect these other bus speeds. If you run your PCI bus too high, it can damage other devices in your system, including wiping out the data from your hard drive.

For example, if you increase the front side bus from 66 to 75 MHz, the PCI bus will run at 37.5 instead of the normal 33, and the AGP bus will run at 75 instead of the normal 66. This is a relatively small increase which normally does not cause any problems, but if you go to a 83 MHz bus, it can get dangerous.

The same applies if you increase from 100 to 112 MHz. This is a small increase which is usually okay. But if you go above that, the same risk exists.

Another thing you need to know is that many CPUs are what is called multiplier locked. Taking our example again of a 233 MHz CPU, it is designed to run at 3.5 x 66 = 233. You cannot change the multiplier because it is locked and will refuse to run at the higher speed. Therefore you are only left with increasing the bus speed which can only be increased so much for above mentioned reasons. But this gives you a bigger performance increase because not only is the CPU running faster, also other parts of the system are, while when increasing the multiplier, only the CPU is running faster.

A good rule of thumb is this:
If you run at a 66 MHz bus, going to 75 MHZ is almost guaranteed to work. Going to 83 is dangerous.

If you run a 100 MHz bus, going to 112 is normally no problem, while anything above that is dangerous.

That said, you need to find out now what multipliers and bus speeds your motherboard supports and how you change those settings. Some motherboards have jumpers that you need to change. These are tiny little plastic covered clips that are placed over pins on the motherboard. They are tricky as they have the annoying habit to jump out of your fingers and disappear in the smallest nooks and crannies.
Other motherboards have actually an option in the BIOS where you can change these settings via a menu which is a lot more convenient. Again, consult your motherboard manual for specifics on your system. You might need a BIOS upgrade to support higher bus speeds and/or multipliers. Go to your motherboard manufacturer’s web site for more details on this.

After reading this and consulting your motherboard manual, you should be able now to either change the jumpers or the BIOS to overclock your CPU.

Please remember:

  • Be realistic and go only one step at a time. After increasing, run your PC for some time, run your most often used programs and make sure that everything runs properly. If you get crashes or other weird behavior, it was not meant to be and you should go back to the previous setting.
  • Back up all your data on your hard drive before doing this. As I said before, if you go too high, there is the danger of losing your hard drive data.
  • If the PC won’t even boot, it doesn’t mean that you broke anything. You can always go back to the previous setting and it should boot up fine.
  • Don’t immediately overclock a brand-new CPU. You should leave it running 24/7 for at least a week to “burn it in”. Your chances of successful overclocking are a lot higher.
  • If if just does not work at all, it was just not meant to be. Not all CPUs overclock well. Some are better than others.

Okay, now you are all set. Have fun, experiment without getting crazy, don’t give up if the first try won’t work, and enjoy if it works. To find out what performance increase you got, I suggest that you run a benchmarking program such as Wintune before and after overclocking for comparison.

For more great information about overclocking, check out the MaximumPC Overclocking section at


– Alex –

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