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[ The PC Guide | Troubleshooting and Repair Guide | The Troubleshooting Expert | Troubleshooting Specific Components | Troubleshooting the Motherboard and System Devices | System Bus, Resources and Expansion Cards ]

I have a PCI expansion card or video card that is supposed to support bus mastering, but I can't get bus mastering to work

Explanation: PCI bus mastering is supposed to be supported by a video or expansion card, but is not working properly. (Note that problems with IDE hard disk bus mastering is discussed in this section, not here.)

Diagnosis: Bus mastering problems are generally hard to diagnose, and often depend a great deal on the specific card. General problems with bus mastering can be related to the motherboard or BIOS settings.


  • Consult the documentation for the peripheral card carefully. Usually the answer to the problem will be there somewhere.
  • Search your motherboard documentation for any hints as to whether all of your PCI slots support bus mastering, or only some of them. Some early and/or cheaper motherboards only supported bus mastering in some of their PCI slots, but not all of them.
  • Double-check all BIOS settings that are in the PCI / PnP settings group. Make sure that you are not disabling bus mastering, or assigning resources incorrectly to only ISA legacy cards.
  • You may have a resource conflict associated with the card..
  • Troubleshoot the expansion card.
  • Troubleshoot the motherboard.

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