Frequency Change of AGP-Bus. Part I

The frequency change of a bus “video system-chipset” is performed synchronously with the frequency change of FSB-bus (“processor-chipset”) and the frequency of PCI-bus. That’s why, while overclocking your processor, you automatically overclock your video system. Some motherboards are equipped with special dividers which enable to control the frequency distribution on FSB, AGP and PCI buses. In this case you may need to set a switch in the required position before changing the bus frequency. This position should be described in a manual of your motherboard.

If you change the frequency of AGP-bus by the software, the standard value of which is equal to 66 MHz, do not forget that the divider for frequency of AGP-bus depends on the frequency of system bus: if the frequency of FSB-bus is equal to 66 MHz, the divider is equal to 1, for 100 MHz – 2/3, for 133 – 2. Thus, the increasing of bus frequency “processor-chipset” form 100 to 110 MHz will cause the rise in frequency of AGP-bus from 66 to 73 MHz.

To set the frequency of SGP-bus, you can use the parameters “AGPCLK/CPUCLK” or “AGP Clock” which are located in a section “Chipset Future Set” (Advanced Chipset Future). These parameters may have the following standard values: 1/1 (or CPU Host Clock) for a bus frequency of 66 MHz, 2/3 (or CPU Host Clock/1.5) for a system bus of 100 MHz and 1/2 (or CPU Host Clock/2) for a system bus of 133 MHz.