Secret Tweaks

PC Hardware: Free Speed: Overclocking Your PC

Performance Boosting Basics

Want a free speed boost for your computer? Try a little overclocking--an enthusiast trick that PC tweakers have been using for years to get free speed out of their systems. Many of today's CPUs can run faster than they're rated to do, and getting that added performance is simply a matter of carefully changing some settings. Overclocking won't turn an ancient PC into a powerhouse, but it can help you squeeze every drop of performance out of your machine.

Two variables set the speed at which your CPU runs: the system bus speed, and the CPU's clock multiplier. To determine the CPU's actual operating speed, those two values are multiplied together. For instance, a bus speed of 100 MHz and a multiplier value of 5.5 translate to a CPU running speed of 550 MHz. This simple formula works with most Intel Celeron, Pentium II, Pentium III, and Pentium 4 chips, as well as with AMD chips.

Some motherboard and CPU combinations let you change one or both of those variables, setting a new speed for the CPU. Boost either setting and you're officially overclocking. In my experience, most CPUs and motherboards will run fine when overclocked 10 to 20 percent faster than the rated CPU speed. The bus speed setting may also affect the speed of the PCI or AGP bus, depending on which chip set the motherboard uses and how that chip set connects to all of the subsystems on the board.

The trick to overclocking is in knowing when to stop. Crank up the speed completely beyond the operating limits of the CPU, system bus, or RAM, and the PC will crash or freeze a lot. If you've set the clock too high on a system that holds the clock settings in BIOS, it may fail to boot, and you'll have to use the PC Setup program to reset the clock settings stored in CMOS RAM. (In some cases, you may have to reset the CMOS RAM more directly: Either remove the CMOS memory retention battery, typically a button-style cell, or move a jumper on the system board; that jumper is often marked 'clear CMOS'.) If your PC uses switches or jumpers to set clock and multiplier values, you'll simply need to reset them to a slower speed.

Utilities like NVidia's NTune, among others I'll discuss below, make it easy to play around with settings, test them, and store certain configs for special occasions--say, when you want a power boost to win in Half-Life 2.

Some systems (mostly the name brands, such as Dell, Gateway, HP, IBM, and Sony) and many Pentium I, II, and III CPUs simply cannot be overclocked; the manufacturers hard-code clocking values into the components to minimize support calls.

CPU Overclocking the Easy Way

Most after-market motherboards built within the past three to four years, such as those from Abit, Asus, MSI, or Tyan, have CPU clock settings available in the PC Setup program stored in the BIOS chip. As your PC boots, an on-screen message should indicate which key you hold down to enter the PC Setup program. Your motherboard manual should explain how to find the parameters that control CPU speed.

The PC Setup program screen in Figure 1

Figure 1: Example of overclocking settings in a PC Setup program.
is from an Abit KA7 motherboard that offers lots of overclocking controls when the CPU Operating Speed is set to 'User Define'. The CPU FSB/PCI Clock setting also affects the speed of the PCI bus. I have found that most PCI cards will overclock about as well as the average CPU does.

Overclocking the AMD Athlon XP+ 2600 processor on my ECS KT-600A motherboard involves just one setting. The multiplier in the Athlon XP+ 2600 processor is fixed at 11.5, allowing a CPU speed range between 1910 MHz (166 x 11.5) and 2288 MHz (199 x11.5). The Athlon XP+ 2600 runs at 1900 MHz typically, but the chip I tested worked well when overclocked to 2200 MHz.

CPU Overclocking by the Bits

Before designers made CPU speed settings changeable via software, switches or jumpers on the motherboard controlled the speed. You'll find this arrangement typical of early (3 to 4 years old or older) AMD, Pentium I and II, and Celeron boards. Overclocking with switches and jumpers works in the same way as using settings in PC Setup: You simply increment the multiplier and bus speed settings to speed up the processor until you find a reliable running speed.

The pictures in Figure 3

Figure 3
and Figure 4
Figure 4
, above, show the jumper posts for the CPU's frontside bus speed, with options ranging from 100 MHz to 110 MHz. You can see the reference chart for the bus speed jumper settings silk-screened on the board (don't count on such a map being on the board--chances are you'll need a manual handy to properly set the jumpers and DIP switches). The CPU clock speed setting also affects the AGP bus speed on this board. Other motherboards use DIP switches (Figure 4
Figure 4
) for both the CPU clock speed and the multiplier settings.

Video Overclocking Made Easy

Most of the overclocking buzz is not about turning a PC into a supercomputer. Instead, it's about gamers being able to see, navigate, run, and shoot faster and smoother. Not surprisingly, you can overclock the processors on your graphics card in much the same way you would your main CPU. Video gaming has come a long way since Pong first appeared on TV-style monitors in the early 1980s. Even if you don't play video games, boosting the performance of your graphics system can enhance the enjoyment of videos and business presentations.

Your graphics speed boost comes from within, without your having to pop the case. To start, simply download the appropriate graphics board hacking tool for the brand of card you have. NVidia has even built overclocking settings into its latest drivers. To enable them, open the Windows Registry editor by going to Start, Run, typing regedit, and pressing Enter. Navigate to "HKEY_LOCAL_MACHINE/SOFTWARE/NVIDIA Corporation/Global/NVTweak/," right-click the right pane of the editor and choose to add a new DWord called coolbits. Edit that entry and give it a hex value of 3, then close your Registry editor. The NVidia tab (Figure 5

Figure 5: Overclocking an NVidia GPU.
) under your PC's advanced display properties settings will now feature a "Clock Frequency Settings" page that allows you to adjust memory and graphics chip clock speeds for your board. Click the "Detect Optimal Frequencies" button if you want the utility to try to find safe overclocked settings for your graphics board.

PC Benchmarks Tell the Speed Story

Sometimes the performance boost you get from overclocking will be obvious. But to see exactly what you've gained, you'll want to benchmark your processing power, memory transfer rates, graphics performance, and hard-drive speed.

PC industry analysts and reviewers test overall PC performance with comprehensive, high-end programs such as PC World's own WorldBench 5 suite ($249) and VeriTest's benchmarks (free). Hobbyists and hackers will often use SiSoftware's Sandra utility suite ($40) or FutureMark's $20 3DMark and $20 PCMark to get more granular analyses.

SiSoftware's Sandra (Figure 2

Figure 2: Performance testing with Sandra.
) provides a huge amount of information about your system's CPU, memory, and I/O devices. It also includes a wide range of performance tests. I like to use Sandra for a quick gauge of my CPU, memory, and hard-drive speeds. For graphics I use FutureMark's 3DMark, which runs numerous tests of critical graphics presentation features, including different types of rendering and texturing, yielding a final aggregate 3DMark score. Running 3DMark is a video show in itself--you watch scenes from different video games and see displays of complex graphics. The combination of Sandra and 3DMark will give you a detailed reference point for judging your hacks.

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