Preventing PCI Resource Conflicts on Intel-Based Computers

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Article ID: 148501 - View products that this article applies to.
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On your Intel-based (x86-processor-based) computer running Windows NT, after you add another PCI device, the system stops responding (hangs) or the PCI device may fail to operate.


The Windows NT Hardware Abstraction Layer (HAL) HAL assigned an I/O port address or memory resource for the new PCI device that overlaps with an existing PCI device therefore causing a PCI resource conflict on your system.

Under normal operation, the system BIOS is responsible for setting the PCI device resource requirements. When Windows NT loads, the Windows NT HAL sometimes moves the PCI device resources. PCI devices are dynamically configurable. However, the Windows NT HAL sometimes assigns overlapping I/O port addresses or memory resources for the PCI devices.


To resolve this problem, upgrade to Windows NT 4.0 and follow the instructions under Windows NT 4.0 Upgrade Information below. To work around this problem use one of the workarounds below.

Windows NT 4.0 Upgrade Information

Under Windows NT 4.0, an option has been added to the BOOT.INI file that the x86-based HALs can recognize. Note that only those HALs shipped by Microsoft will recognize this switch. When a HAL recognizes the /PCILOCK switch (option), the HAL does not allow the operating system to change the PCI device resources as long as the system BIOS settings appear to be correct and complete.

If the adding of a PCI adapter causes a hang during boot, remove the offending PCI adapter card. Reboot the system and modify the BOOT.INI file by adding the /PCILOCK option. Shut down the system, add the new adapter card, and reboot the system.

The Windows NT 4.0 HALs that currently have this fix in are: HAL.DLL, HALMPS.DLL, and HALAPIC.DLL.


To work around this problem, do one of the following:
  • Insert the PCI adapter cards to a different PCI slot. This option does not apply to PCI devices built in to the main system board (motherboard).

  • Change the driver load order for the conflicting PCI adapters. This is not always possible when the types of drivers loaded have to be in a pre-determined order. Be very careful when modifying the registry as an incorrect setting may cause the system to become unstable or unbootable.


Microsoft has confirmed this to be a problem in Windows NT versions 3.5 and 3.51. Microsoft has corrected this problem in Windows NT 4.0 and in the latest Windows NT 3.51 U.S. Service Pack. For information on obtaining the Service Pack, query on the following word in the Microsoft Knowledge Base (without the spaces):


When you write device drivers for Windows NT, remember that the call to HalAssignSlotResources is the API that moves the PCI resources. Some drivers use IoReportResourceUsage, as a HalAssignSlotResources alternative, with the current resource settings obtained from the configuration space of the PCI device. The calls to HalGetBusData and HalGetBusDataByOffset can be used to read the PCI device configuration space. This method should only be used as a last resort as it contradicts the purpose of having a dynamically configurable bus.


Article ID: 148501 - Last Review: November 1, 2006 - Revision: 2.1
  • Microsoft Windows NT Workstation 3.5
  • Microsoft Windows NT Workstation 3.51
  • Microsoft Windows NT Workstation 4.0 Developer Edition
  • Microsoft Windows NT Server 3.5
  • Microsoft Windows NT Server 3.51
  • Microsoft Windows NT Server 4.0 Standard Edition
kbhardware KB148501

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