Make your PC go faster for free

Posted on 3 Jul 2009 at 12:03

• 
• 
• 

 1 of 3

Gallery

The most obvious solution would seem to be to leave the external bus speed alone and adjust the processor's multiplier, increasing its speed without touching any other component's speed. However, this isn't possible on most processors, as the multiplier is usually locked. Only AMD's Black Edition and Intel's Extreme Edition processors have unlocked multipliers.

Safety first

To prevent your memory having errors when it's overclocked, there are a couple of things to try in your BIOS. First, you can adjust the memory's voltage setting. Increasing the memory voltage by 10 per cent should do the trick. For DDR2 RAM, this would mean increasing it from 1.8V to 2.0V. If this fails, then there's one last thing you can try that might save the day: adjusting the memory ratio. By lowering this, it's possible to increase the external bus speed but keep the memory running at close to its normal level.

Adjusting the memory ratio can be tricky, as BIOSes can display this figure in different ways. The easiest BIOSes to use let you adjust the ratio and also display the resulting speed in MHz of the memory. This makes it easy to adjust, as you can increase the external bus's speed and see how fast your memory is running and adjust the memory ratio accordingly.

Unfortunately, not all BIOSes are that easy to use. We've seen plenty that only let you select the type of memory you have installed (DDR2 667MHz, DDR2 800MHz and so on), without displaying the current speed at which the memory is running. The way to deal with these situations is to work out the ratios at default settings manually. Remember, the ratio is the memory's full rated speed divided by two to give the memory frequency, then divided by the external bus speed. With our Intel processor it has a 200MHz external bus, so running DDR2 800MHz memory gives us a ratio of 2:1 (800 ? 2 = 400, 400 ? 200 = 2). The same settings running DDR2 667MHz would give us a ratio of 1.67:1 (667 ? 2 = 333, 333 ? 200 = 1.67).

With DDR2 800MHz memory, increasing the external bus speed by 20 per cent to 220MHz increases the memory speed to 880MHz. Selecting the DDR2 667 option in the BIOS would reduce memory speed to 735MHz (220 x 1.67 = 367.4, 367.4 x 2 = 735MHz). At this level our memory would be running more slowly than normal, so this probably isn't a good choice in this instance. Just be aware that exceeding our recommended maximum of a 20 per cent increase could cause problems with memory, so you may need to lower its ratio.

Another bus comes along

The final complication with adjusting the external bus is that it also affects the system bus, which the processor uses to communicate with other devices in your system. For all Intel processors, bar the Core i7, there's a quad-pumped frontside bus (FSB), which runs four times faster than the external bus speed. In our example, then, our E5200 processor has a 200MHz external bus and an 800MHz FSB (200 x 4). This multiplier is fixed, and if you increase the external bus too much, you'll run into problems.

AMD and Core i7 processors don't have an FSB, but use HyperTransport and QuickPath Interconnect respectively. These newer buses let the processor talk directly to each component, rather than sharing the FSB, as with older Intel processors. The speed of these buses is controlled by an adjustable multiplier. For example, an AMD processor with a 1,800MHz HyperTransport bus has a 9x multiplier (200MHz external bus x 9).

The good thing about this system is that, depending on your BIOS, you can increase the external bus speed but reduce the multiplier. To maintain stability, you should ideally keep these bus speeds at their default level. Before you start overclocking, make a note of the system bus's default speed - then, when you adjust the external bus, lower the multiplier until the system bus runs at a similar speed to its default level.