Am I joining this thread correctly?

I have some additional questions on PCI steering. Recently when I installed a Viper 550 video
card it appeared at IRQ 11 with two IRQ holders. When the system proved to be quite touchy I
found device manager with no conflicts, but HW Diagnosis indicated that the devices "IRQ holder
for PCI steering" were both "had a problem". Eventually I stumbled upon the method to disable
PCI steering. This cleared out the problematic IRQ holders, but the Windows added some back,
even though PCI steering remains disabled. Now HW Diagnosis indicates no problems, the
Diamond card shares IRQ 11 with a modem and an IRQ holder and the system appears more
stable.

My questions: What did this PCI steering conflict really indicate? and Is my current configuration
really stable? Ken Warm

> 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
>
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