Overclocking Guide

by Anand Lal Shimpi on April 30, 1997 7:24 AM EST
What is Overclocking?

Also known as speed margining, overclocking is the process by which you increase system performance via the increasing of one of two things:

1) CPU Clock Rate
2) Bus Speed

Why should I Overclock?

If you want an easy inexpensive way to increase overall system performance (though not always the safest way) Overclocking is right for you. First, I would like to state that I am not responsible for any damages caused to your system caused by information obtained from this page or any page. You must first realize that there is a certain risk involved with overclocking, you risk shortening the lifespan of your computer as a whole as well as system stability. Overclocking should be done at your own risk and expense, again I am in no way responsible for possible system damage caused by overclocking. Now that we got that out of the way lets find out how to overclock...

Overclocking - The Tools of the Trade

So you want to overclock, but what do you need? First you need adequate cooling, be sure to have a fairly large heatsink and fan combo. A little Thermal Compound between the heatsink and processor wouldn't hurt either. Second, you need to find out the jumper settings for your specific mainboard. These can be found out from the mainboard manual or from the manufacturer's web page. Third, if you wish to overclock the bus speed (i.e. taking it up to 66MHz or above) make sure your mainboard supports the specific bus speed and make sure you have RAM that will handle the increased load. I recommend 60ns EDO for any bus speed above 60MHz, and SDRAM for any bus speed above 75MHz. Some tweaking of the BIOS memory timings may be necessary to ensure stable system performance. Now that we've taken care of that, lets move on to how you overclock...

Overclocking - The Basics

As stated above you have two options once you've decided to overclock your system (actually now there are three options but I'll get to the third one a little later). You can increase the CPU's rated clock speed or you can simply increase the memory bus speed. First let's talk about increasing the CPU's rated clock speed. This can be accomplished by increasing the CPU clock multiplier with or without increasing the memory bus speed. For example, lets take a Pentium Classic running at 150MHz. The bus speed of this chip is a mere 60MHz with a 2.5x clock multiplier, this gives you a multitude of possibilities to overclock to. Lets discuss the options you would have in this situation. You could simply increase the clock multiplier from 2.5x to 3.0x resulting in a 180MHz processor and a nice little performance gain. You also have the option of increasing the clock multiplier and bus speed taking it from a 60MHz bus times a 2.5x clock multiplier to a 66MHz bus speed times a 3.0x clock multiplier therefore giving you a whopping 200MHz chip. The latter scenario I should add is REALLY pushing the limits of the chip and should be approached with caution. Earlier I discussed the option of simply increasing the memory bus speed. In this case, doing so would yield an extremely fast processor. Increasing the bus speed from 60MHz to 66MHz would take the chip up to a whopping 166MHz and resulting in an overall system performance increase of around 15% - 25%. The stability of the system in this case would be much more reliable than overclocking the CPU to 180 or 200MHz since you are only increasing the actual CPU clock rate by 16MHz versus 30 or 50MHz.

Basic Overclocking Table

Below is a list of the first and second options when performing a basic overclocking of your CPU (NOTE: the AMD K5 PR/166+ runs using a 1.75x internal clock multiplier and the AMD K6 PR2/233 uses an internal 3.5x clock multiplier):

CPU Bus Speed Clock Multiplier Option 1 Option 2
AMD K5 PR/75+ @ 75MHz 50MHz 1.5x 66 x 1.5 = 100MHz 60MHz x 1.5 = 90MHz
AMD K5 PR/90+ @ 90MHz 60MHz 1.5x 66 x 1.5 = 100MHz N/A
AMD K5 PR/100+ @ 100MHz 66MHz 1.5x N/A N/A
AMD K5 PR/133+ @ 100MHz 66MHz 1.5x N/A N/A
AMD K5 PR/166+ @ ~116MHz 66MHz (Internal) 2.5x N/A N/A
AMD K6 PR2/166MHz 66MHz 2.5x 66 x 3.0 = 200MHz N/A
AMD K6 PR2/200MHz 66MHz 3.0x 66 x 3.5 = 233MHz N/A
AMD K6 PR2/233MHz 66MHz (Internal) 1.5x 66 x 4.0 = 266MHz N/A
Cyrix 6x86 PR90+ @ 80MHz 40MHz 2.0x 50 x 2.0 = 100MHz N/A
Cyrix 6x86 PR120+ @ 100MHz 50MHz 2.0x 55 x 2.0 = 110MHz N/A
Cyrix 6x86 PR133+ @ 110MHz 55MHz 2.0x 60 x 2.0 = 120MHz N/A
Cyrix 6x86 PR150+ @ 120MHz 60MHz 2.0x 66 x 2.0 = 133MHz N/A
Cyrix 6x86 PR166+ @ 133MHz 66MHz 2.0x N/A N/A
Intel Pentium 100MHz 66MHz 1.5x 66 x 2.0 = 133MHz 60 x 2.0 = 120MHz
Intel Pentium 120MHz 60MHz 2.0x 60 x 2.5 = 150MHz 66 x 2.0 = 133MHz
Intel Pentium 133MHz 66MHz 2.0x 66 x 2.5 = 166MHz N/A
Intel Pentium 150MHz 60MHz 2.5x 66 x 2.5 = 166MHz N/A
Intel Pentium 166MHz 66MHz 2.5x 66 x 3.0 = 200MHz 60 x 3.0 = 180MHz
Intel Pentium 180MHz 60MHz 3.0x 66 x 3.0 = 200MHz N/A
Intel Pentium 200MHz 66MHz 3.0x 66 x 3.5 = 233MHz N/A
Intel Pentium 233MHz 66MHz 3.5x N/A N/A
Intel Pentium II - 233MHz 66MHz 3.5x 66 x 4.0 = 266MHz N/A
Intel Pentium II - 266MHz 66MHz 4.0x 66 x 4.5 = 300MHz N/A
Advanced Overclocking
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