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mike@mikeshardware.co.uk

Overclocking

So, you have purchased a motherboard capable of adjusting your CPU's clock multiplier, unlocked the clock multiplier of your CPU whilst building your machine, found a spare hard drive and installed a copy of Windows 9x, Motherboard Monitor and a 3D game onto it. We are now ready to see what your CPU is capable of!

Overclocking on a KT7/KT7-RAID

If you have an Abit KT7 or KT7-RAID then overclocking is a fairly straightforward task. Go into your BIOS by holding down the Del key when starting your machine, and enter the 'Softmenu III Option' menu. If you have successfully unlocked your clock multiplier you will be able to adjust the CPU Operating Speed entry. The adjustment of this option along with changing the CPU Power Supply from 'CPU default' to 'User define' and adjusting the core voltage is the primary method of overclocking your processor.

The default Core voltage for (newer) Duron processors is 1.6v, although the KT7 will allow you to change this value between 1.1v and 1.85v in 0.025v steps. Increasing the core voltage will allow your processor to run at a higher speed, but it will also increase the temperature of the CPU. Although 1.7v is considered by AMD to be the maximum voltage for the Duron CPU, its brother the AMD Athlon has a maximum voltage of 1.85v and a default voltage of 1.75v. The only difference between these processors is the quantity of on-board L2 cache (64Kb on the Duron and 256Kb on the Athlon), so it can be assumed that a Duron running with a 1.85v core voltage is safe, provided your cooling is adequate.

Before we start overclocking we need to make sure that our cooling is sufficient. The Duron and Athlon processors are rated to operate at up to 90deg C, although their lifespan at this temperature would not be very long! If your CPU is shown (in the BIOS) to be running at these sort of temperatures, you have not affixed your Heatsink correctly - disassemble the machine and put it right before you do permanent damage! A safe maximum temperature should be around 60deg C. Note that this is an absolute maximum though. A non-overclocked CPU should be running in the low to mid 40's, with an overclocked CPU perhaps running in the high 40's or low 50's.

If you have purchased a high quality heatsink and fan and your CPU temperature is acceptable when running at its default core voltage, you may like to increase the core voltage to its maximum (1.85v) straight away. If you are like me, however, you may prefer to take it easy and go a couple of core voltage steps at a time. The basic technique is as follows:

1. Run a 3D game or other CPU intensive application at the CPU's default values for about an hour. If everything is stable (which it should be!) check the CPU temperature and make sure it is acceptable.

2. Increase the clock speed by 50Mhz (behind the scenes this is achieved by increasing the clock multiplier by 0.5)

3. Boot into Windows.

4. If this was successful, go back to Step 2. If this wasn't successful then go back into the BIOS and up the core voltage by 0.5v. Go back to Step 2.

Once you have reached 1.85v with the CPU temperature still within acceptable limits, and you have failed to boot into Windows you need to drop the CPU speed back down by 50Mhz. At this point you need to do some serious stability testing. Run your chosen CPU intensive program for 30mins and check your temperature. If all is Ok you need to leave your machine on test for at least an extra hour to determine stability. Ideally you need to keep the core voltage as low as possible, so you may like to try to minimise this whilst keeping stability high.

Here are the results from my overclocking:

As you can see, my Week 25 Duron 650 managed to get to 900Mhz - not bad for a week 25 CPU, but newer CPU's should be able to get to at least this level and possibly up to 1Ghz. The Heatsink and Fan used was a Globalwin FOP32-1. I used the default thermal pad which came with the CPU, although applying my own thermal paste may well have kept the temperatures down a little more!

Although you can further boost your performance by increasing the front side bus speed, I personally am not that bothered about doing so. If you wish to try this then you should note that each 1Mhz increase in FSB speed will increase the speed of your CPU by (CPU Speed/100)Mhz. It is also worth noting that the VIA KT133 chipset is likely to have problems with FSP speeds more than 10Mhz over the default 100Mhz (Remember that the Athlon's bus is double-pumped to the equivalent of 200Mhz, i.e. data is transferred over both the rising and falling clock edges).

Now that we have managed to overclock our CPU, it is useful to see how much of a difference our overclocking has made to the speed of our system. As this site is primarily associated with 3D graphics performance, the most representative benchmark would be that of a 3D game. One of the better 3D games for benchmarking is Quake 3. Here are the results of our overclocking on a Quake 3 timedemo:

The demo runs at 640x480x16 to minimise the effect of the graphics card (A GeForce SDR) on the demo. The benchmarking was done by executing the following command four times and taking the highest recorded FPS:

quake3 +seta r_mode 2 + seta r_fullscreen 1 +seta r_swapinterval 0 +vid_restart +s_soundinit 0 +snd_restart +timedemo 1 + demo demo001

We have managed to achieve a Frames Per Second increase of 13% by overclocking our Duron 650 to 900Mhz. This is reasonable increase, but perhaps not the level which we would like for our 38% CPU clock speed increase. Let us see if we can boost our performance even more by optimising our BIOS settings.

BIOS Optimisation