7/13/2006

A Guide to Overclocking Your CPU

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Introduction to Overclocking


I remember the first time I had decided to overclock my computer. Although I am tech savvy, overclocking was an area I was concerned about since it could potentially damage or destroy my computer. For this reason I read as much information on the subject as possible to make sure I had a firm grasp on overclocking. An issue I ran into initially was that most of the articles I read made assumptions, either that I had a certain type of CPU, or that I knew the difference between Front Side Bus overclocking and overclocking through the CPU Clock Multiplier. I make none of these assumptions in this tutorial. If you already know these technical details, simply skip over the sections you're familiar with. The aim of this guide is to walk you through overclocking any CPU or video card, no matter how old or new, or which vendor produced the product.

Use Caution


At a very basic level overclocking refers to running a processor or component at a faster rate than it was designed for. This can yield better performance, but comes with the risk of overheating and potentially destroying the component. It is advisable to monitor the temperature of the component that you're overclocking to make sure that it is within acceptable temperatures. To minimize the risk of burning the chip out, special heatsinks, fans, and even water cooling systems are sometimes used as replacement for the stock heatsinks. Another pitfall that comes with overclocking is that the lifespan of the product may decrease, since it is processing quicker than it is was designed to operate. This can also void the warranty for your processor, and even your RAM and other system components.

There are a few points I'd like you to consider while reading this article and tweaking your system. The first point is that overclocking can damage your system, so don't overclock if you're not prepared for the possibility of your system getting fried. This brings me to the second point; do everything in moderation. If you want to avoid frying your system, take things nice and slow, and don't try to push the envelope. If you really want to became an extreme overclocker, I still recommend making baby steps until you've got a bit of experience under your belt. When you overclock you should keep an eye on your temperatures. A good program for doing that is Motherboard Monitor, available for free.

Each CPU family has a different range of maximum temperatures, here is a large table of CPU's and their maximum temperatures. I must warn you that I've seen 2 different AMD Athlon XP's reboot over and over again when reaching temperatures as low as 60c. This is far lower than what's recommend on that page. When in doubt, again play it safe. You should verify the official heat rating for your CPU at either Intel's site or on AMD's site. Most CPU's can achieve a decent overclock with their stock heatsink, but acquiring after market heatsinks specifically designed for overclocking can keep your system nice and cool while achieving some amazing overclocks.

The Basic Methods of Overclocking


Overclocking through the CPU Clock Multiplier is perhaps one of the easiest methods. The CPU Clock Multiplier is the number of cycles your CPU does during one tick of the front side bus. For example, my frontside bus runs at a speed of 166MHz, and my CPU Clock Multiplier is 11.5, meaning that each time my front side bus completes a cycle at 166MHz, my CPU has completed 11.5 cycles during that time. That gives me an effective speed of 1909Mhz (166 * 11.5 = 1909.) Now if I were to raise the CPU clock multiplier I would overclock the CPU. For example, changing my multiplier to 12.5 would overclock me to 2075MHz (166 * 12.5 = 2075.) Unfortunately, some CPUs ship with the CPU multiplier locked, however there are some work arounds for specific processor families. Here's a good guide to unlocking the Athlon XP Thoroughbred and Barton CPUs. Here's another method for unlocking Athlon XPs that also covers Palomino chips.

The other main method for overclocking a CPU is to increase the Frontside Bus Speed. For example, if I were to increase my FSB from 166 to 200, my CPU would run at 2300MHz (200 * 11.5 = 2300.) Now adjusting the frontside bus doesn't just overclock your CPU, but also everything else that uses the bus, including your RAM. This is both a good and a bad thing. You can get better performance out of your whole system, but you might bottleneck your ability to overclock the CPU due to the performance limitations of your RAM and other components. Using my system as an example again, my frontside bus runs at 166MHz which is 333MHz DDR. Now the type of RAM that is rated 333MHz is PC2700, so what I did was purchase the next step up, PC3200, which is rated for DDR speeds of upto 400MHz. By doing that, I insured that my RAM would be able to handle bus speeds as high as 400MHz, giving me 66MHz of headroom to overclock.

Another thing to consider is that when overclocking the frontside bus on some systems, you will automatically overclock the PCI and AGP bus as well. This is actually a bad thing because it can cause system instability. I recommend using either an ATI or nVidia nForce based chipset on your motherboard. If you're using a VIA based chipset than carefully test your system each overclock to make sure that the PCI and AGP bus can handle it.

The level of success you have with overclocking will depend entirely upon the specific hardware that you have. Unfortunately some motherboards do not allow you to adjust the front side bus speed, and some CPUs and motherboards do not allow you to increase the CPU Multiplier. Hopefully you either purchased your motherboard/CPU combination specifically because you could overclock it, or you lucked out and your BIOS has those settings. If not, there's still hope. Wolfram Podien, a German programmer, created a program which allows you to change the front side bus speed using a different technique using the System Management Bus. The program, unfortunately is shareware, and cost $13 to register. The shareware version can be downloaded here. If you find that your motherboard doesn't support overclocking, check out this article I wrote which explains how to use CPUFSB.

Well, now that you know the basics of how overclocking works, the actual act of overclocking is pretty simple. If your motherboard's BIOS supports overclocking through the front side bus, it's just a matter of changing the bus speed to your desired level. Or if you're overclocking the cpu multiplier, just remember that FSB times your CPU Clock Multiplier equals you effective speed. Once again you should do this cautiously, gradually increasing the speed of your CPU, rebooting, and then testing the stability of Windows as you progress. There are some programs designed specifically (or just happen to great) for stressing your system to make sure that it is stable. One such program is Prime95 which I recommend you download and use the "Torture Test" after each overclock. If running Prime95 makes your system crash, than your overclock is not stable enough for daily computing activities.

Links of interest:
http://www.neoseeker.com/Articles/Hardware/Guides/OCguide/
http://wiki.extremeoverclocking.com/wiki/Main_Page

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