PCI Clock Synchronization Mode

Common Options : To CPU, 33.33 MHz, Auto

Quick Review of PCI Clock Synchronization Mode

The PCI Clock Synchronization Mode BIOS feature allows you to force the PCI bus to either synchronize itself with the processor FSB (Front Side Bus) speed, or run at the standard clock speed of 33.33 MHz.

When set to To CPU, the PCI bus speed is slaved to the processor’s FSB speed. Any change in FSB speed will result in a similar change in the PCI bus speed. For example, if you increase the processor’s FSB speed by 10%, the PCI bus speed will increase by 10% as well.

When set to 33.33 MHz, the PCI bus speed will be locked into its standard clock speed of 33.33 MHz. No matter what the processor’s FSB speed is, the PCI bus will always run at 33.33 MHz.

The Auto option is ambiguous. Without testing, its effect cannot be ascertained since it’s up to the manufacturer what it wishes to implement by default for the motherboard. But logically, the Auto setting should force the PCI bus to run at its standard speed of 33.33 MHz for maximum compatibility.

It is recommended that you set the PCI Clock Synchronization Mode BIOS feature to To CPU if you are overclocking the processor FSB up to 12.5%. If you wish to overclock the processor FSB beyond 12.5%, then you should set this BIOS feature to 33.33 MHz.

However, if you do not intend to overclock, this BIOS feature will not have any effect. The PCI bus will remain at 33.33 MHz, no matter what you select.

Details of PCI Clock Synchronization Mode

When set to To CPU, the PCI bus speed is slaved to the processor’s FSB speed. Any change in FSB speed will result in a similar change in the PCI bus speed. For example, if you increase the processor’s FSB speed by 10%, the PCI bus speed will increase by 10% as well.

When set to 33.33MHz, the PCI bus speed will be locked into its standard clock speed of 33.33 MHz. No matter what the processor’s FSB speed is, the PCI bus will always run at 33.33 MHz.

The Auto option is ambiguous. Without testing, its effect cannot be ascertained since it’s up to the manufacturer what it wishes to implement by default for the motherboard. But logically, the Auto setting should force the PCI bus to run at its standard speed of 33.33 MHz for maximum compatibility.

Synchronizing the PCI bus with the processor FSB allows for greater performance when you are overclocking. Because the PCI bus will be overclocked as you overclock the processor FSB, you will experience better performance from your PCI devices. However, if your PCI device cannot tolerate the overclocked PCI bus, you may experience issues like system crashes or data corruption.

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. Still, you should test the system thoroughly for stability issues before committing to an overclocked PCI bus speed.

Please note that if you wish to synchronize the PCI bus with the processor FSB and remain within this relatively safe limit, you can only overclock the processor FSB by up to 12.5%. Any higher, your PCI bus will be overclocked beyond 37.5 MHz.

If you wish to overclock the processor FSB further without worrying about your PCI devices, then you should set this BIOS feature to 33.33 MHz. This forces the PCI bus to run at the standard speed of 33.33MHz, irrespective of the processor’s FSB speed.

However, if you do not intend to overclock, this BIOS feature will not have any effect. The PCI bus will remain at 33.33 MHz, no matter what you select.

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PCI Clock Synchronization Mode – The Tech ARP BIOS Guide