AMD Athlon Overclocking Guide

Unlike the clock multiplier and voltage controls, the L2 cache divider is not controllable by the Athlon’s feature connector.  This means that if you wish to adjust the speed of your L2 cache, even if you have an Athlon overclocking card, you’re going to have to resort to physically modifying your Athlon’s PCB. 

Why would you want to adjust the L2 cache divider?  By default, all Athlon CPUs running at 700MHz or below are set to a 1/2 L2 cache divider, meaning the L2 cache runs at 1/2 the speed of the core.  Everything faster than 700MHz runs its L2 cache at 2/5 the CPU speed due to a lack of affordable and readily available L2 cache that can operate at speeds greater than 350MHz.

For example, let’s take an Athlon 500 equipped with 4ns L2 cache.  Let’s say that the core of the Athlon 500 would have no problem hitting 600MHz, but using the 1/2 L2 cache divider that would put the L2 cache at 300MHz.  Using our little formula for figuring out L2 cache speed in MHz (MHz rating = (1 / (4ns x 10^-9)) / 1000000) ) using the ns rating, we come up with the fact that 4ns L2 cache is theoretically capable of running at 250MHz.  So at 600MHz, although the CPU itself can get up that high, the L2 cache would be the limiting factor as it might not be able to operate at this high of a frequency. 

Now if we could adjust the L2 cache divider from 1/2 to 1/3, a divider supported by the Athlon (you can only use supported dividers, such as 1/2 1/3, 2/5), then the L2 cache would be running at 600MHz * 1/3 or 200MHz, below what it’s rated for.  So you can see how being able to adjust the L2 cache divider can have its benefits towards overclocking.  Until recently, you were only able to adjust the L2 cache divider by physically modifying the Athlon’s PCB.

An individual who goes by the name of H. Oda has been developing FSB related tweaking software for quite some time (i.e. SoftFSB), and is the author of WCPUID, a program that many people use to measure their actual clock speed and L2 cache frequency.  H. Oda recently released the first version of WCPUA2 software that allows for the control of the L2 cache divider in Windows.