At 14:06 1/28/99 -0500, Michelle Thuma wrote:
>I looked at my devices ordered by IRQ, and there is one other device
>using the same IRQ: IRQ holder for PCI steering. Does anyone know what
>this is, and would it be causing the conflict?

It is perfectly normal to have one or more instances of "IRQ Holder
for PCI Steering" in Device Manager.

In Win95 and Win95a (OSR1), the IRQs assigned to PCI devices by the
motherboard BIOS could not be changed. With Win95b (OSR2), a feature
called "PCI bus IRQ steering" was added which enables Windows to
override the IRQ assigned by the BIOS to any PCI device. Windows
can give IRQs to PCI devices that are normally given to Plug and Play
ISA devices. This gives Windows flexibility in rebalancing Plug and
Play PCI and ISA resources around non-Plug and Play ISA devices.

When Windows is loading and decides that it must give a PCI device a
different IRQ from the one already assigned to it by the system BIOS,
it first disables the PCI device and then goes about obtaining an IRQ
for it by reprogramming an ISA type IRQ to a PCI type IRQ. It assigns
an IRQ holder to this IRQ which is used during the time that the PCI
device is being reenabled and given the newly reprogrammed IRQ.

As an example of how this all works, suppose your computer's BIOS
is unaware of non-Plug and Play ISA cards and you are using either
the original Win95 or Win95a. If the BIOS has set a PCI device to
IRQ 10, you may have a resource conflict when you add a non-Plug and
Play ISA device that is configured for IRQ 10.

However, with PCI bus IRQ steering, Windows can resolve this IRQ
resource conflict. To do so, Windows first disables the PCI device
and reprograms a free IRQ to be a PCI IRQ, for example IRQ 11.
Then it assigns an "IRQ holder" to IRQ 11 and then moves the PCI
device to IRQ 11. Finally it reprograms IRQ 10 to be an ISA IRQ
and removes the IRQ holder for IRQ 10.

If an IRQ Holder for PCI Steering is displayed when you view the
System Devices branch of Device Manager, it indicates that an IRQ has
been programmed to PCI mode and is *unavailable for ISA devices*,
even if no PCI devices are currently using that IRQ.

If you go to Device Manager and double-click the System Devices
branch, then the PCI Bus, and then click the IRQ Steering tab, you
should see either "IRQ Steering Enabled" or "IRQ Steering Disabled".
You can turn it on or off.

Regards,
Bill

         The PCBUILD web site always needs good submissions.  If
          you would like to contribute to the website, send any
               hardware tech tips or hardware reviews to:
                           [log in to unmask]