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BIOS and Overclocking

The BIOS of the ASUS P4P800S mainboard, as well as of every recent product from ASUS, is based on AMI microcode. Moreover, thanks to the software compatibility of the i848P and i865PE chipset, ASUS didn’t develop a brand new BIOS from scratch. The BIOS of the ASUS P4P800S is mainly based on the BIOS of the well-known product, ASUS P4P800. Accordingly, they have nearly identical BIOS Setup settings.

For example, the BIOS Setup of the ASUS P4P800S features AI Overclocking technology, which allows speeding up the system by 30% (depending on the processor and memory modules) without any specific effort. The BIOS Setup contains options like Overclock 5%...Overclock 30%, which simply increase the FSB frequency to this value. However, I would advise you to leave this option alone. You’d better set the AI Overclock option to “Manual” to get access to all overclocking parameters. They include:

  • FSB frequency overclocking. Formally, the range is 100-400MHz. Recalling that Intel processors have a fixed multiplier, this very high upper limit for the FSB frequency is nothing, but a promotional move. None of the available processors would work at such a high FSB frequency. 

  • Memory frequency adjustment. The memory frequency will depend on the FSB frequency. The following table lists the available options:
  • FSB

    Memory bus (BIOS value)

    FSB:MEM dividers


    266 MHz



    266 MHz
    333 MHz



    266 MHz
    320 MHz
    400 MHz


    Note that the BIOS Setup of the ASUS P4P800 can show only nominal frequencies for the memory (DDR266, DDR333 and DDR400). The effective memory clock-rate at non-standard FSB frequencies is chosen with respect to the CPU multiplier and doesn’t correspond to the number displayed in the BIOS Setup. You should keep this in mind when overclocking your system. For example, if you set the memory bus to 400MHz in the BIOS Setup and then increase the FSB frequency, you will automatically increase the memory frequency, too. And the latter fact won’t be reflected in the BIOS Setup in any way.

  • AGP/PCI frequencies can be set to the following values: Auto, 66.66/33.33MHz, 72.73/36.36MHz and 80.00/40.00MHz. It means you don’t have to worry about the PCI/AGP frequencies when overclocking the FSB. Just set them up as high as you think would be good and forget about them.

  • CPU voltage can be adjusted manually. The range stretches from the nominal CPU voltage to 1.95V with 0.025V increment. This range should be considered quite wide.

  • Vdimm can be set to Auto, 2.55V, 2.65V, 2.75V and 2.85V.

  • Vagp may vary from 1.5V to 1.8V with 0.1V increment.

The Advanced Chipset Settings page of the BIOS Setup contains the memory timings.

Here, you can adjust DRAM CAS# Latency (available values – 2, 2.5 and 3), DRAM Precharge Delay (5, 6, 7 and 8), DRAM RAS# to CAS# Delay and DRAM RAS# Precharge (2, 3 and 4).

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