PCI Video Adapter May Not Function on Secondary PCI Bus

This article was previously published under Q236030
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On a computer with two PCI buses that are joined by a PCI-to-PCI bridge, a PCI video adapter that is placed on the secondary PCI bus may not function properly. You may experience any of the following symptoms:
  • The video adapter is not recognized at the hardware level.
  • Windows NT 4.0 may report parity errors while it is loading the video drivers.
  • Video distortion may occur.
  • The secondary video adapter is not detected while you are configuring multiple monitor support in Windows 2000 or Windows 98.
This behavior can occur if the computer's BIOS does not correctly set the VGA Enable and ISA Enable bits on the PCI bridges. If the BIOS does not correctly set these bits on the PCI bridges, a resource conflict can occur between the bridges.
To resolve this issue, contact the manufacturer of the BIOS to inquire about obtaining a BIOS revision that configures the VGA Enable bit and the ISA Enable bit properly for the PCI bridges.

As a workaround, you may be able to install the PCI video adapter in one of the slots on the primary PCI bus. Consult your computer documentation to determine which PCI slots make up the primary bus on your computer.
The issue discussed in this article is a hardware problem; contact your hardware manufacturer for additional information. The hardware manufacturer may not support certain PCI devices beyond the PCI-to-PCI bridge.

The industry-standard PCI bus architecture limits a single bus to three PCI slots. Additional PCI slots are on a separate PCI bus and must go through a PCI-to-PCI bridge. On a computer that has a primary and secondary bus joined by a PCI-to-PCI bridge, the primary bus has only two PCI slots available; one slot is used for the PCI-to-PCI bridge. The PCI-to-PCI bridge is actually a PCI translator that decodes and encodes address calls that are being passed upstream from, or downstream to, the secondary PCI bus. This process is managed by the computer's BIOS.

For additional information about configuring the PCI-to-PCI bridge, visit the following Microsoft Web site:For additional information about preventing PCI resource conflicts and troubleshooting multiple monitors, click the article numbers below to view the articles in the Microsoft Knowledge Base:
148501 Preventing PCI Resource Conflicts on Intel-Based Computers
170922 How PCI Devices Are Detected and Why They May Fail
238886 How to Set Up and Troubleshoot Multiple Monitors in Windows 2000
multimon display

Article ID: 236030 - Last Review: 10/21/2013 22:49:25 - Revision: 3.4

  • Microsoft Windows 2000 Server
  • Microsoft Windows 2000 Professional Edition
  • Microsoft Windows NT Server 4.0 Standard Edition
  • Microsoft Windows NT Workstation 4.0 Developer Edition
  • Microsoft Windows 98 Standard Edition
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