Overclocking the BX6-2

Anyone who builds their own system today is aware of the overclocking potential of the Celeron series. With little tweaking, it's possible to get almost any Celeron 300A to run at 338, 375, or even possibly 450MHz. Doing so potentially keeps these folks from buying high-end Pentium II systems, something which must chaff Intel's hide.

Another potentially more serious problem is CPU remarking - OEMs, resellers, or system integrators may purchase lower-speed parts and overclock them, selling them as faster systems for a higher price. While it sounds outrageous, remarking is actually quite common in the industry, and it's difficult to stop because it's both difficult to find, and to track (since these parts trade hands quite often in the OEM/reselling business).

In experiments as early as the Pentium 166 processor, Intel has always been interested in defeating overclocking. Starting with the Pentium II, Intel has implemented a multiplier lock on their CPUs, which prevents users from adjusting the CPU frequency in relation to the system bus frequency. A 300Mhz part that runs at 66Mhz x 4.5 can no longer be set to 333Mhz (66 x 5.0) or 366Mhz (66x 5.5).

However, Intel has not yet stopped overclocking by bus speed. This means that while the multiplier for a 366Mhz part is locked at 5.5x, the 66Mhz bus speed can still be adjusted, to 75, 83, or 100Mhz. The only problem with this was that the PCI and AGP bus would also be affected by the bus speed, and these components tended to be more sensitive to higher frequency than the CPU or chipset themselves.

With the introduction of the 100Mhz Front Side Bus (FSB), this problem was largely solved. The FSB allowed the main system bus to run at a separate frequency from the PCI and AGP buses. If your CPU was capable of running at 1.5x of its marked speed (the jump from 66Mhz to 100Mhz), then your PCI and AGP components would still be set at their standard 33/66Mhz settings. By placing a Celeron in a 440BX chipset-equipped motherboard, it was possible to boost a 300Mhz chip to 450Mhz by taking advantage of the FSB.