Overclocking an AMD Athlon XP 2600+ Barton Core
By default, the AMD Athlon XP 2600+ comes clocked around 1.9Ghz, and runs on a 333Mhz frontside bus. Now the Barton chips have the mutliplier locked, so the easiest way to overclock is to simply raise the frontside bus speed. Of course you'll need a motherboard that supports higher frontside bus speeds than 333Mhz. For that purpose I baught an Asus A7N8X-E Deluxe, which uses the nVidia nForce2 Ultra 400 chipset. This is an ideal motherboard for overclocking, as it lets you adjust not just the frontside bus speed, but also the multiplier, and the AGP bus speed as well (which you should keep set at 66Mhz.) I made sure to buy PC3200 ram that is designed to run at 400Mhz, even though my CPU runs at 333Mhz. This gave me enough headroom to overclock my CPU without worrying that the RAM would bottle neck it. Just for the sake of comparison, I tested some PC2700 memory in the system as well. I also baught the Aero Cool Hightower heatsink, which works excellently, and I used 3dMark 2005's CPU test for a basic benchmark.
So here's my system specs:
AMD Athlon XP 2600+ Barton
ASUS A7N8X-E Deluxe
1GB PC3200 + 512MB PC3200 set to aggressive memory timings
AeroCool Hightower CPU Heatsink
The Athlon XP 2600+ seems to overclock very nicely, and I slowly stepped it up from 166 up to 180 FSB. Windows booted fine so I continued, this time to 189. Once again Windows booted perfectly, so I decided to stress my CPU out a bit and play Half Life 2 for awhile. Still no problems. Next I tried increasing the FSB up to 196 This time Windows wouldn't boot, so I went into the bios and barely increased the voltage to the CPU by 0.25 (you always want to be careful when messing with the voltage; last thing you want is a fried CPU!) This got me back into Windows, but Half Life 2 triggered a reboot. I tried lowering it back down to 193, while keeping the extra voltage I had adjusted in the BIOS. This time Windows booted fine, and Half Life 2 ran great.
So in the end, I did manage to get it to the AMD Athlon 2600+ barton overclocked to about 2.3Ghz, but it just wasn't stable enough for me. Even at 2.2Ghz 3dMark 2005 wasn't stable enough for me. I've settled on a median of about 2.2Ghz for now. It's the perfect way to squeeze a little more performance out of my aging computer, with only a small risk of damaging the processor.
UPDATE: I was cruising the internet and I found this excellent beginners guide to overclocking, if anyone's interested.