My system has a few of these. Can anyone explain in simple terms, please:-
What is it?
Do I need it?
I have one on the same IRQ as my video card, and 2 on another IRQ. If not needed, how do I remove them?
fobotcso
26th Aug 2001, 20:24
BOAC: Try this from Microsoft. Suggest you leave well alone.
SUMMARY
=======
This article describes Peripheral Component Interconnect (PCI) bus interrupt
request (IRQ) steering.
MORE INFORMATION
================
Windows 95 OEM Service Release 2 (OSR2), Windows 98, Windows 98 Second Edition,
and Windows Millennium Edition (Me) provide support for PCI bus IRQ steering. By
using PCI bus IRQ steering, Windows can dynamically assign or "steer" PCI bus
IRQs to PCI devices. Note that Microsoft Windows 95 (retail release) and
Microsoft Windows 95 OEM Service Release 1 (OSR1) do not provide support for PCI
bus IRQ steering.
ISA and PCI IRQs
----------------
Multiple Industry Standard Architecture (ISA) devices cannot share an ISA IRQ;
however, multiple PCI devices can share a PCI IRQ. On computers that use a PCI
bus, the 16-standard IRQs can be programmed to either PCI or ISA mode. An IRQ
cannot be programmed for both modes at once.
How IRQs Are Assigned to PCI Devices
------------------------------------
In Windows 95 (retail release) and OSR1, the basic input/output system (BIOS)
assigns IRQs to PCI devices. With OSR2 and Windows 98, Windows 98 Second
Edition, and Windows Me, if PCI bus IRQ steering is disabled in Windows the BIOS
assigns IRQs to PCI devices, but if PCI bus IRQ steering is enabled, Windows
assigns IRQs to PCI devices. When IRQ steering is enabled the BIOS still assigns
IRQs to PCI devices and, even though Windows can change these settings, it
generally does not.
CardBus Cards and OSR2
----------------------
PCI R3 Personal Computer Memory Card International Association (PCMCIA) cards
(CardBus cards), look very similar to the more common ISA R2 PCMCIA cards.
CardBus cards use 32-bit addressing and require a PCI-type shareable IRQ. R2
PCMCIA cards use 16-bit addressing with an ISA-type non- shareable IRQ. PCI bus
IRQ steering gives the operating system the flexibility to reprogram PCI IRQs
when it rebalances Plug and Play resources. Without PCI bus IRQ steering,
Windows can rebalance only Plug and Play ISA IRQs to resolve resource
conflicts.
How OSR2 and Windows 98, Windows 98 Second Edition, and Windows Me Use PCI Bus IRQ Steering
-------------------------------------------------------------------------------------------
PCI bus IRQ steering gives Windows 98, Windows 98 Second Edition, and Windows Me
the flexibility to reprogram PCI interrupts when rebalancing Plug and Play PCI
and ISA resources around non-Plug and Play ISA devices. Windows 95 (retail
release) and OSR1 cannot rebalance PCI and ISA IRQs for Plug and Play devices
around non-Plug and Play ISA devices to solve resource conflicts.
For example, if your computer's BIOS is unaware of non-Plug and Play ISA cards,
the operating system does not have PCI bus IRQ steering, and 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 the operating system can resolve this IRQ
resource conflict. To do so, the operating system:
- Disables the PCI device.
- Reprograms a free IRQ to a PCI IRQ, for example IRQ 11.
- Assigns an IRQ holder to IRQ 11.
- Moves the PCI device to IRQ 11.
- Reprograms IRQ 10 to be an ISA IRQ.
- Removes the IRQ holder for IRQ 10.
IRQ Holder
----------
An IRQ Holder for PCI Steering may be displayed when you view the System Devices
branch in Device Manager. An IRQ Holder for PCI Steering indicates that an IRQ
has been programmed to PCI mode and is unavailable for ISA devices, even if no
PCI devices are currently using the IRQ. To view IRQs that are programmed for
PCI-mode:
1. Click Start, point to Settings, click Control Panel, and then double-click
System.
2. Click the Device Manager tab.
3. Double-click to expand the System Devices branch.
4. Double-click the IRQ Holder for PCI Steering that you want to view, and then
click the Resources tab.
How to Determine If Your Computer Is Using IRQ Steering
-------------------------------------------------------
To determine if your computer is using IRQ Steering:
1. Click Start, point to Settings, click Control Panel, and then double-click
System.
2. Click the Device Manager tab.
3. Double-click to expand the System Devices branch.
4. Double-click PCI Bus, and then click the IRQ Steering tab. You should see
either the IRQ Steering Enabled or IRQ Steering Disabled settings.
NOTE: PCI bus IRQ steering is disabled by default in OSR2. If you are using OSR2
and IRQ steering is disabled, verify that the Use IRQ Steering check box is
selected on the IRQ Steering tab.
IRQ Steering may be displayed as disabled in Device Manager for any of the
following reasons:
- If the IRQ routing table that must be provided by the BIOS to the operating
system may be missing or contain errors. The IRQ routing table provides
information about how the motherboard is configured for PCI IRQs.
- If the Use IRQ Steering check box is not selected.
- If the "Get IRQ table from Protected Mode PCIBIOS 2.1 call" check box is not
selected.
- If your computer's BIOS does not support PCI bus IRQ steering. For more
information, contact the manufacturer of your BIOS.
Now I hope all this is abundantly clear!
Absolutely clear, FOBOTCSO! Just don't ask me any questions!
PS You are one heck of a good source of info!
Think I'll take your advice and walk away whistling.
Many thanks
BOAC
Hew Jampton
27th Aug 2001, 21:25
When I used the McAfee utilities thing, it used to bleat about "IRQ Holder for PCI Steering Disabled" as if it was a serious fault, and it could not autorepair it. After much hassle and searching round, I found out that it was no such thing.