Pentium III Issues

Bus Speed and Multiplier

Compared to the latest Celerons, the Pentium III processors all have relatively low multipliers because they're designed to operate on the 100MHz FSB instead of the Celeron's 66MHz bus. This poses a serious problem for aspiring P3 overclockers. As many may already know, Intel clock locks the multiplier and the only way to overclock current Intel processors is to increase the bus speed.

Unfortunately, most boards offer only a handful of bus speeds above 100, and even Abit boards neglect the higher +100 bus frequencies. Newer boards do offer more bus speeds between 100 and 133, but we still aren't seeing any of the small 1 MHz ticks yet.

Our Abit BE6 motherboard has these FSB options above 100MHz: 105, 110, 112, 115, 120, 124, 133, 140, 150. The BE6 offers both 1/3 and 1/4 dividers for the 124 and higher frequencies in case some of your peripherals aren't overclock friendly, but the motherboard doesn't offer many of the 100+ bus speeds available on the BX6-2, most notably the 117, 129, and 138 speeds. It would be nice to have the 117, 129, and 138 settings available.

You also have to be careful with the AGP bus. Most motherboards only offer a 1/1 or 2/3 AGP clock ratio. This is fine if you're only using the standard 66MHz or 100MHz bus, but overclocking the Pentium III requires us to use frequencies higher than 100MHz.

RAM and L2 cache

With all these >100MHz bus speeds, that 10ns PC100 RAM isn't going to cut it anymore. You might still be able to use your PC100 RAM depending on the speed of the memory. Modules with 8ns RAM can support bus speeds up to 125MHz (1000/8 = 125), and PC133 RAM has 7.5ns (1000/7.5=133.33) or faster memory. Most memory modules should have the speed rating on each chip; look for a -75, -8, or -10. You can usually rely on this method to check the speed of the chips, but some manufacturers might use deceiving product numbers. Note that not all chips rated 7.5ns and faster are automatically accepted as PC133.

The type of cache may also affect the processor's ability to overclock. Currently, Toshiba, Samsung, and Mitsubishi all supply cache for the P3. Pentium III processors are also finicky about the L2 cache latency. Increasing the L2 latency value isn't an option anymore. Setting the L2 latency above 8 disables the cache.