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Performance Guide: Intel Pentium III

Overclocking Coppermine

Classical overclocking by chosing a higher multiplier is not possible any more for years now. Let me give you a short explanation:

The processor speed (or core speed) is always generated by the system clock speed (or FSB: Front Side Bus), which today is 66, 100 or 133 MHz, multiplied with 1.5, 2.0, 2.5, 3.0 etc. Today, multpliers of 4.0, 4.5, 5.0... and up to 8.0 are widespread. Example: A Pentium II 450 runs at 100 MHz FSB x4.5 (multiplier). The Pentium III 800 is available in two versions: The Pentium III 800E runs at 100 MHz x8.0, while the 800EB uses 133 MHz x6.0. A Celeron 500 uses 66 MHz FSB x7.5.

The easiest way to overclock a processor is running it at a higher clock speed than specified (by increasing the multiplier). This was still possible with the Pentium classic, Pentium MMX and most Pentium II processors. A few years ago however, Intel and AMD made this kind of overclocking impossible by locking the multiplier of each CPU. There are some tricks around that multiplier lock in case of Athlon processors, but nobody has found a viable solution to unlock Intel processors yet.

Athlon processors can be overclocked by changing the multiplier ('all you need' is to open the processor cartridge and plug-on an Athlon overclocking board ), Intel CPUs can merely be overclocked by rising the bus speed. As you may know from The 150 MHz Project, Part 1 and The 150 MHz Project, Part 2 , this can become quite a touchy affair. When overclocking a processor by clocking it higher, the only component which had to endure the higher clock speed was the CPU itself. Rising the system bus speed means accelerating North Bridge, PCI, AGP, main memory and other devices as well, thus increasing the failure rate considerably.

Running A 100 MHz CPU At 133 MHz FSB

Coppermine is available in 100 MHz FSB versions between 600 and 850 MHz. Many boards allow to run the CPU at 133 MHz FSB, which results in a much higher core speed:

Official Speedat 100 MHzMultiplierSpeedat 133 MHz FSB
550 MHz5.5733 MHz
600 MHz6.0800 MHz
650 MHz6.5866 MHz 1
700 MHz7.0933 MHz 1
750 MHz7.51000 MHz ²
800 MHz8.01066 MHz ²
850 MHz8.51133 MHz ²

1 This setting is very likely to fail, but with some luck and excellent cooling it may work
² This setting will most likely not work reliably at all.

Of course you may do the same with Katmai CPUs, but the chance of success is indeed very small: A Pentium III 450 would have to bear 600 MHz, which should be possible with proper cooling (particularly the L2 cache chips will run far beyond their specs). I don't think that the 500 MHz model will run at the 667 MHz (clocked with 133 MHz FSB). Don't think about trying this with the 550 and 600 MHz type of Katmai - your system won't even start up.