HANDS ON GUIDE

Step 7: A big FSB

With the multiplier at 9, the PC wouldn't remain stable beyond a 400MHz FSB but, as I could drop the multiplier, I started to think about trying for a higher FSB with a lower multiplier. I knew the CPU was stable at 3.6GHz, so with a multiplier of 8, it should take an FSB of 450MHz. The advantage of a high FSB is that it creates enormous bandwidth, something from which encoding tasks benefit massively. However, you need the memory to cope with it, so I swapped out the Kingston RAM for some Corsair 1,066MHz PC2-8500 modules, which are good for an FSB of 533MHz (or more if overclocked) with a 1:1 ratio.

With the multiplier set to 8, the PC was happy with a 450MHz FSB, but wouldn't load Windows. Drat. The first step was to increase the FSB termination voltage to 1.4V - this voltage supports the FSB and comes in very handy when you're a long way above the 266MHz default. The change meant that we could get into Windows, but the PC still wouldn't benchmark stably. Next, we tried pumping up the Northbridge voltage; as it's the Northbridge through which the FSB runs, this is always a good bet if an overclock fails. Even at 1.55V, the PC wouldn't behave. Eventually, we found that setting the CPU voltage to 1.5625V allowed the system to run stably. When you're pushing an overclock, gradually working your way through the voltage settings is a good way to make the system stable, but don't become too trigger-happy with the many settings modern motherboards offer you.

Given the trouble we had with a 450MHz FSB, it wasn't surprising that dropping the multiplier to 7 caused gremlins to appear. The PC booted with a 500MHz FSB, but wasn't stable. Clearly, 450MHz x 8 was the best I would achieve without water-cooling the CPU and possibly the Northbridge too. However, with a 450MHz FSB and a clock multiplier of 8, the CPU ran at 3.6GHz, 33 per cent faster than its stock clock speed, and my benchmark scores rocketed. Not bad for an afternoon's work.

Problem alert: If your PC crashes when it’s overclocked, reboot it. Many modern motherboards will recover well, but always check that the board has saved your overclocked settings. Sometimes, after a crash, the board will revert to its factory settings without alerting you. If your PC crashed and won’t restart, you need to clear the CMOS, which will reset the BIOS to its defaults. Turn off the PC at the wall, and find the CLEAR CMOS jumper. Move the jumper to the correct pins (this will be shown in the manual), wait ten seconds, then move it back and power up again.

Latest Hands on guides

These are the most popular features articles over the past three months.

Mobile Broadband

Compare prices

Fastest, cheapest 3G mobile broadband dongles from 3, Vodafone, T-Mobile and Orange
from just £10/month