Performance Guide: Intel Pentium III

Intel 440BX Vs. I820/i840 Vs. VIA 694X

Both the i820/i840 chipsets as well as the VIA Apollo Pro 133A (VT82C694X) are officially designed for 133 MHz operation. This means that they feature all necessary AGP and PCI dividers to derive the required 66 MHz AGP and 33 MHz PCI speed from the system bus speed. It's a bit more touchy with BX motherboards. BX does only know the AGP dividers 1/1 and 2/3 (for 66 and 100 MHz FSB), but the PCI dividers 1/2, 1/3 and 1/4, while the latter is basically meant for 133 MHz FSB (using 1/4 PCI clock will have the PCI running at 33 MHz). Nevertheless, the AGP will run at 2/3 FSB speed (89 MHz in case of 133 MHz FSB), which some graphics cards won't accept.

Older BX motherboards (> 12 months) are usually not suited for 133 MHz at all, because the PCI divider 1/4 is missing since it never meant to be used. That's why the PCI-bus would run at 44 MHz, which is obviously far too much for most devices.

If you want to run a 133 MHz Coppermine on a BX motherboard, make sure the following:

  • The AGP graphics card will have to be able to run at 89 MHz AGP clock speed. Take a look at: Exploration into Overclocked AGP Graphics .
  • Make sure you are using brand PC133 SDRAM
  • Your motherboard will have to support PCI divider 1/4 to run it at 33 MHz. Else you will get trouble with most PCI cards!