IRQ Conflicts with PCI Display Adapters

• Microsoft Windows 95

SYMPTOMS

When you install a Peripheral Component Interconnect (PCI) video adapter that is configured to use a particular interrupt (IRQ), Windows 95 may configure it to use another IRQ that is already in use by another device.

CAUSE

PCI devices can share PCI IRQs, but Windows 95 does not support sharing PCI IRQs with other non-PCI devices (such as an IDE controller).

Windows 95 display drivers do not use an IRQ. However, PCI adapters request an IRQ for full backward compatibility.

RESOLUTION

Use Device Manager to resolve the conflict by assigning a different IRQ to one of the conflicting devices.

MORE INFORMATION

This behavior is common to all PCI display adapters, but does not apply to Industry Standard Architecture (ISA) or VESA Local Bus (VLB) display adapters.

PCI devices can share IRQs. This behavior is in the PCI specification and Windows 95 supports it. PCI devices must be configured by the computer's BIOS. This occurs during the computer's Power-On Self Test (POST) before the operating system is loaded. Windows 95 does not configure PCI devices, but uses what the BIOS reports.

In order to get full Plug and Play functionality, Windows 95 enables inactive devices when it starts. For example, if a second IDE controller is disabled in the BIOS but not in Device Manager, the controller is enabled and resources are assigned to it. To prevent this behavior, disable the inactive device and remove it from the current configuration in Device Manager.

Note that if you are using an early version of the Micron BIOS, you should contact Micron for a later version. Early versions of the Micron BIOS do not configure PCI cards correctly, leading to conflicts with the video device on IRQ 15 or other non-valid IRQs. To correct this problem, Micron recommends that you upgrade the ROM BIOS to revision 19. You can obtain the ROM BIOS flash upgrade from Micron, or from Micron's Web site at:

   http://www.mei.micron.com