Be sure to read Part 1 of our Athlon Buyer's Guide

When we first took a look at a final production version of AMD's Athlon CPU on a fully functional Slot-A motherboard, one of our initial reactions was, "Hey, you can't overclock this thing." A quick call to AMD revealed that they had taken a different approach to controlling the clock multiplier and voltage settings of the Athlon CPU than the market had been used to. Instead of allowing for the two options to be controlled and adjusted on the motherboard as they have been in the past, AMD placed the only method for controlling the clock multiplier and core voltage on the Athlon processor card itself.

This manipulation is done by a physical modification of a combination of 16 resistor slots on the processor card. A number of Taiwanese websites published the first instructions on the actual manipulation of a few of these resistors to increase the clock multiplier of the processor, but Dr. Thomas Pabst of Tom's Hardware Guide was actually the first to produce a complete guide on all of the available settings, including the settings for changing the core voltage. The guide is very well written and contains all of the background information necessary to know how one can physically overclock the Athlon, so take a look at it if you are truly interested.

Since the release of that article, many individuals that are a little more than skilled with their soldering irons have taken it upon themselves to make a few bucks off of the modification. The fact of the matter is that when AMD released the Athlon back in August, they could already hit 750MHz in their own labs, so it makes perfect sense to expect that the Athlon is at least a decent overclocker. At the same time, the higher clock speed Athlons are out of the price range of many, while the Athlon 500 weighs in at a very competitive and reasonable price. What do these two events have in common? Take an Athlon 500, overclock it to 650MHz, and you now have a 650MHz Athlon for around $250.

Unfortunately, the modification process is very dangerous and should be reserved for those with quite a bit of experience with delicate soldering techniques. This is where the idea of capitalism comes in: at an added premium, a number of companies are offering pre-overclocked Athlon CPUs that operate at the higher speeds but cost lower than the higher clocked part would go for. Is there anything wrong with this? Not at all, as long as the vendor discloses that these CPUs are in fact overclocked and there are risks involved.

Some individuals have even taken it to the next level and have actually outfitted their modified Athlon CPUs with a set of dip switches that can control the clock multiplier and core voltage so that the control is placed back in the hands of the user. We were lucky enough to obtain an evaluation sample from one of these individuals, Mark Sorensen, the owner and operator of Trinity Micro. Trinity Micro is currently offering a modified Athlon 500 for $310, as well as the opportunity to have your own CPU modified for $125.00 + shipping and handling. While the pricing may seem quite steep, we had tremendous success with our evaluation Athlon 500, as you're about to see. Note that this potential does not apply to Trinity Micro's Athlon units alone, as they are all using the same chips, just different methods of modifying them in order to achieve the common goal: taming and overclocking the world's most robust x86 CPU.

The yields on the Athlon have been incredible; they are high enough that some users are reporting that their lower clock speed Athlon CPUs feature L2 cache chips that would be normally found on the higher speed CPUs. One such case was that of our Athlon 500 evaluation unit from Trinity Micro which featured 3.6ns L2 cache, normally reserved for 600MHz Athlon CPUs.

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With the L2 cache capable of hitting the 300MHz required at a 600MHz clock speed, it came to no surprise that our Athlon 500 evaluation unit made it up to 600MHz without even the slightest hiccup. By increasing the core voltage to 1.75v we were able to get the Athlon to POST at 800MHz. Keep in mind that this is from a 500MHz CPU and we disabled the L2 cache in order to test the core itself.

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Unfortunately, the problem with this method is that disabling the L2 cache significantly decreases performance in most applications and the raw clock speed increase then only serves as a benefit if you're running a 3D game or another similar application that is not L2 cache dependent. Luckily, there is a way to adjust the L2 cache divider by a method similar to the one used to adjust the clock multipliers and it allows you to change the L2 cache divider from the default /2 (1/2 * clock speed) to /3 or even /1 for a 1:1 L2 cache to core clock speed ratio.

While the latter option isn't really feasible since we would need at least 2ns L2 cache in order to even hit the 500MHz requirement of an Athlon 500 with a 1/1 L2 cache divider, the 1/3 multiplier makes quite a bit of sense. If your L2 cache is the limiting factor with the overclocking potential of your CPU (this can be determined by turning off the L2 cache, and seeing how far your CPU will overclock, then turning it back on and seeing how far it will go then) it may be worth it to settle for the slower 1/3 speed L2 cache but at the higher core clock speed.

So how do you control the L2 cache divider on the Athlon? We already know all of the other settings for clock multiplier and voltage from Tom's Article and below are the settings for the various L2 cache frequency dividers:

Using R103, R104, R106 and R107 located on the back of the Athlon card, the settings are as follows:

What are the tradeoffs of the lower L2 cache clock speed versus the higher core clock speed? That's what we're here to find out, but first let's take a look at the options offered to us by Trinity Micro's modified Athlon.

Starting with Overall System Performance, measured by BAPCo's SYSMark 98, the precedence seems to be given to the setups with the higher overall clock speed. The Athlon overclocked to 750MHz with a 250MHz L2 cache (1/3 * 750 = 250MHz) outperforms the Athlon 700 with its 350MHz L2 cache and the Athlon 700 with 233MHz L2 cache outperforms the Athlon 650 with 325MHz L2 cache.

The performance of overclocked Athlons is a very positive sign for owners of slower CPUs whose L2 cache cannot cope with speeds much greater than 300MHz. Imagine purchasing an Athlon 500 that could overclock to 700MHz easily, with the only necessary tweak being that you reduce the L2 cache speed to 233MHz from your original 250MHz. The performance benefit is definitely worth it. But does this trend continue as we explore the individual applications SYSMark 98 uses to derive its score?

All scores are Time in Seconds, Lower is Better