Overclocking the Pentium III

The FiringSquad labs were only able to grab hold of one Pentium III 500, so remember the usual disclaimer: overclocking depends greatly on the manufacturing quality of each individual processor, and what works or doesn't work here may not necessarily be the case for you.

Turning to Abit, creators of the overclocker's dream, the BH6, I was able to talk to Steve Lee, who had just finished testing with a new BIOS, BH6_HN. He was kind enough to send us a copy to flash our in-house BH6 to support the Pentium III, and also confirmed our reports of the 32KB L1 cache. Once the BIOS was updated, we booted up and made a bee-line straight for Soft-CPU II.

P3 Operating Temperature - Open Case Ambient Temp 19.2°C
CPU speed	Temperature
Pentium 3 - 620	47.8°C
Pentium 3 - 560	47.1°C

The Pentium III, like the Pentium II and Celeron line before it, is multiplier-locked, which means that the only way to overclock it is by adjusting the bus frequency. This doesn't come as much of a surprise - Intel has yet to find a way to lock the bus frequency, or set the chip to only operate between certain frequencies. It does mean that the Pentium III has a good chance of overclocking to a 112MHz FSB, and very likely even higher once 133MHz and Direct RDRAM are released later in the year.

So, how fast were we able to push the P3? Try 620MHz. At a 5.0x multiplier and 124MHz bus clock speed, I was really surprised to see the processor POST, only to crash immediately afterwards. Increasing the voltage to 2.10v, and then 2.20v, the same happened. Thinking this was more of a strain on our CAS-3 RAM than the CPU itself, I removed one of the two 64MB PC100 DIMMs, and tried again. This time, the system booted!

While it wasn't exceptionally stable at that frequency (anyone want to send us some 7ns DIMMs?), our processor was able to eke out a few tests before crashing. I thought about pushing the processor even further, but decided against it for now. I did manage to get a couple of benchmarks to give you an idea of what a 600+ MHz CPU can offer.

It was apparent that the CPU or the RAM couldn't take a 124MHz FSB, so I lowered it to 5.0 x 112MHz, at 2.0v -- the system posted and booted without a hitch. The 560MHz is a very respectable overclock for a top-of-the-line CPU. The P3 remained completely stable at 560, and we've included benchmark scores at this speed on the ABIT motherboard.

For the remainder of the testing, we turned to our trusty standby, the rock-solid Supermicro P6SBA. When we contacted SuperMicro, they were more than happy to give us access to their beta BIOSes as well. With everything going well, I began to set up our labs for testing.