PCI Clock / CPU FSB Clock

Common Options : 1/2, 1/3, 1/4, 1/5, 1/6

Quick Review

This BIOS feature allows you to manually select the PCI bus clock divider. Because this divider determines the speed that the PCI bus will run at, manipulation of this feature allows you some control over the PCI bus speed.

It was meant to keep the PCI bus running within specifications when you overclock the processor bus but you can also use it to overclock the PCI bus. With that said, you should keep in mind that the recommended safe limit for an overclocked PCI bus is 37.5 MHz. This is the speed at which practically all new PCI cards can run at without breaking a sweat.

Selecting the clock divider of 1/2 makes the PCI bus run at half the processor bus speed. As such, this clock divider is useful for processor bus speeds of 66 MHz to 75 MHz.

Selecting the clock divider of 1/3 makes the PCI bus run at a third of the processor bus speed. As such, this clock divider is useful for processor bus speeds of 100 MHz to 112.5 MHz.

Selecting the clock divider of 1/4 makes the PCI bus run at a quarter of the processor bus speed. As such, this clock divider is useful for processor bus speeds of 133 MHz to 150 MHz.

Selecting the clock divider of 1/5 makes the PCI bus run at a fifth of the processor bus speed. As such, this clock divider is useful for processor bus speeds of 166 MHz to 187.5 MHz.

Selecting the clock divider of 1/6 makes the PCI bus run at a sixth of the processor bus speed. As such, this clock divider is useful for processor bus speeds of 200 MHz to 225 MHz.

You will probably be wondering about the gaps in the processor bus speeds listed above. For your convenience, only processor bus speeds that produce PCI clock speeds within the range of optimal PCI clock speeds (33 MHz to 37.5 MHz) are displayed above. The other processor bus speeds will either produce a slow PCI bus or an excessively overclocked one.

Therefore, for optimal PCI bus performance, try to strike for one of the processor bus speed-divider combinations shown above.

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