Overclocking the Athlon XP

As we've mentioned earlier, multiplier x FSB = clock speed. We already know the FSB is adjustable, but normally, the multiplier is not. If you have a multiplier of 15, and your CPU's FSB is normally 133MHz, your chances of hitting 200 FSB are not that great.

By lowering the multiplier, your chances are better, but your milage will vary depending on the CPU stepping. Newer steppings (or core revisions) tend to be easier to overclock because AMD refined the manufacturing process.

The goal here is typically to increase the clock speed, but there will be instances where increasing the FSB will net better performance at lower clock speeds. Confused? Don't worry, we'll explain as we head into the BIOS.

Adjusting the Multiplier

Almost any decent motherboard worth it's weight will allow you to adjust the multiplier of an unlocked CPU in the BIOS. In rare cases, you may have to switch a jumper. Sometimes, such as with the DFI LANParty KT400, you'll need to switch from 133 to 166 (and up) to gain access to the higher FSB settings.

The location of the CPU adjustment settings in the BIOS vary from manufacturer to manufacturer, but typically, the multiplier options will be in the Advanced Chipset Features.

The only exception is the ABIT series of motherboards which rely on the Soft Menu III.

In either case, the multiplier options will be greyed out until you select an "Expert", "Manual" or "User Define" setting. This will open up all the tweak options you'll need for overclocking.

By selecting the Multiplier (or something similarly named) option, you'll have a choice of what multiplier you want to use.

Normally, we suggest taking a lower multiplier, something in the 9.5 - 12 range, but this is something you'll have to experiment with until you find a comfortable balance between the multiplier and FSB. Now, if you have a low stock multiplier, you might try moving it upwards and see how that does. In anycase, try not to do drastic jumps, and maybe adjust it 0.5 at a time.

Adjusting the FSB

Unlike the multiplier, which is something we normally suggest you lower, the FSB is something you will to increase. With a lower multiplier, increasing the FSB will be easier. The FSB adjustments can be found in the same screen as your multiplier adjustments. It may say "Front Side Bus", "External Clock" or something along those lines.

Either you'll have to move the cursor up or down, or key in a number within the minimum and maximum range of the motherboard (it will tell you if this is the case). 250 FSB is usually the maximum, but don't go setting it at 250 FSB right off the bat. Like the mulitplier, it's good practice to do a small adjustment, test for stability, and continue.

Important Notes

Overclocking successfully is not just about changing multipliers and FSB. There are a lot of factors to consider, such as your memory, ratios, dividers, and voltages. We stated at the beginning that a higher FSB is usually more effective than increasing the multiplier when overclocking a system. A higher FSB increases the speed of several key components, and the end result is a faster overall computer.

Therefore, while multiplier changes affect the CPU, FSB changes affect the entire motherboard.

Basically, you'll want quality memory, since running syncronously (aka 1/1), which means the memory bus runs at the same speed as the FSB, will push the memory harder. A good motherboard will provide additional ratio options in the cases where your memory can't handle the higher FSB speeds.

If you have PC2700 ram, which is 166MHz, and your CPU can hit 220FSB, I seriously doubt a 1/1 ratio will work. We'll have to run asyncronous, in otherwords, out of sync. Looking at the above image, let's use 4/3 and the aforementioned FSB speeds. At 4/3, your FSB remains at 220, but it gets divided by four, then multiplied by three. The net result for the memory is 220/4 x 3 = 165MHz, well within the memory's limits.

Dividers work the same way, except it deals with your PCI and AGP slots. PCI spots are rated at 33MHz, and AGP at 66MHz. The key is to keep the slots as close to the rated speeds as you can. Some motherboards even allow you to hard set (type in 66 for AGP) the speed, so you don't have to do any math.

Finally, anything running faster will need more power than before. The CPU will almost certainly need additional voltage to maintain stability. Make sure your cooling is up to it though as more power means more heat. Speaking of more power, a quality power supply is a must for successful overclocking. I personally recommend a 350W at the minimum, and anything from Antec, PC Power and Cooling, and Vantec are excellent PSUs.

Given that it isn't always possible to keep the PCI, AGP and memory within spec, even with ratios and dividers, you may need to increase the voltage to those components. Then again, video card and memory overclocking are popular options when jacking up system speed, so you'll need to play with their voltages if this applies to you.

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