Options : Yes, No

If all your operating systems support Plug & Play (PnP), select Yes so that they can take over the management of device resources. If you are using a non-PnP-aware OS or not all of the operating systems you are using support PnP, select No to let the BIOS handle it instead.

Note that Windows 2000 will work with ACPI even with PnP OS Installed set to Enabled. Just make sure you disable Advanced Power Management (APM). This information was contributed by Alex. For more information, check out his e-mail. Alex also provided a link to a Microsoft article on how to setup ACPI support for Windows 98 users (Unfortunately, this link is broken. If you find this article, do let me know so that I can mirror it.). However, Microsoft recommends that you disable PnP OS Installed, just to be safe. Here's the link to the Microsoft article on IRQ sharing in Windows 2000 provided by Ryu Connor.

For Linux users, Jonathan has the following advice -

Although Linux is not really PnP compatible, most distributions use a piece of software called ISAPNPTOOLS to setup ISA cards. If you have PnP OS set to No, the BIOS will attempt to configure ISA cards itself. This does not make them work with Linux, though, you still need to use something like ISAPNPTOOLS. However, having both the BIOS and ISAPNPTOOLS attempting to configure ISA cards can lead to problems where the two don't agree.

The solution? Set PnP OS to Yes, and let ISAPNPTOOLS take care of ISA cards in Linux, as BIOS configuration of ISA cards doesn't work for Linux anyway (with the current stable and development kernels). Most times, it probably won't make a difference, but someone somewhere will have problems, and Linux will always work with PnP OS set to Yes.

Please refer to Comments #80 and #82 for more information on Linux and PnP.

Britt Turnbull recommends disabling this feature if you are running the OS/2 operating system, especially in a multiboot system. This is because booting another OS can update the BIOS which may later cause problems when you boot up OS/2. In addition, if you add/change hardware, you should enable full hardware detection during the initial boot sequence of OS/2 (ALT-F1 at boot blob -> F5, etc...) so that the new hardware can be registered correctly.

Thomas McGuire of 3D Spotlight sent me this e-mail from Robert Kirk at IBM :-

"Actually, the setting "PnP OS" is really misnamed. A better thing would be to say "do you want the system to attempt to resolve resource conflicts, or do you want the OS to resolve system conflicts". Setting the system to PnP OS says that even if the machine determines some kind of resource problem, it should not attempt to handle it...rather, it should pass it on to the OS to resolve the issue. Unfortunately, the OS can't resolve some issues.... sometimes resulting in a lock, or other problems.

For stability reasons, it is better to leave EVERY motherboard regardless of manufacturer set to "PnP OS=no", but still allow the hardware to auto configure PnP devices. Just leave the one setting to always say "PnP OS = no". It won't hurt a thing, you lose nothing, your machine will still autoconfigure PnP devices, and will make your system more stable."

Thanks, Thomas. That was really useful info. With that advice from both IBM and Microsoft, it is highly recommended that you disable this BIOS feature, irrespective of whatever operating system you actually use.

Force Update ESCD / Reset Configuration Data

Options : Enabled, Disabled

ESCD (Extended System Configuration Data) is a feature of the Plug & Play BIOS that stores the IRQ, DMA, I/O and memory configurations of all the ISA, PCI and AGP cards in the system (PnP or otherwise). Normally, you should leave the setting as Disabled.

But if you have installed a new add-on card and the consequent system reconfiguration causes a serious conflict of resources (the OS may not boot as a result), then you should enable it so that the BIOS will reset and reconfigure the settings for all PnP cards in the system during bootup. The BIOS will automatically reset the setting to Disabled the next time you boot.

Resource Controlled By

Options : Auto, Manual

The BIOS has the capability to automatically configure all of the boot and Plug & Play compatible devices. Normally, you should set it as Auto, so that the BIOS can automatically assign the IRQs and DMA channels. All the IRQ and DMA assignment fields should disappear as a result.

But if you are facing problems assigning the resources automatically via the BIOS, you can select Manual to reveal the IRQ and DMA assignment fields. Then you can assign each IRQ or DMA channel to either Legacy ISA or PCI/ISA PnP devices.

Legacy ISA devices are compliant with the original PC AT bus specification and require a specific interrupt / DMA channel to function properly. PCI/ISA PnP devices, on the other hand, adhere to the Plug & Play standard and can use any interrupt / DMA channel.

Assign IRQ For VGA

Options : Enabled, Disabled

Many high-end graphics accelerator cards now require an IRQ to function properly. Disabling this feature with such cards will cause improper operation and/or poor performance. Thus, it's best to make sure you enable this feature if you are having problems with your graphics accelerator card.

However, some low-end cards don't need an IRQ to run normally. Check your graphics card's documentation (manual). If it states that the card does not require an IRQ, then you can disable this feature to release an IRQ for other uses. When in doubt, it's best to leave it enabled unless you really need the IRQ.

Assign IRQ For USB

Options : Enabled, Disabled

This function is similar to USB Controller. It enables or disables IRQ allocation for the USB (Universal Serial Bus). Enable this if you are using a USB device. If you disable this while using a USB device, you may have problems running that device. However, if you don't use any USB devices, set the option to Disabled. It will free up an IRQ for other devices to use.

PCI IRQ Activated By

Options : Edge, Level

This is a rarely seen BIOS feature that allows you to set the method by which the IRQs for your PCI cards are activated / triggered. ISA and old PCI cards are Edge triggered (using a single voltage) while newer PCI and AGP cards are Level triggered (using multiple voltage levels).

When PCI devices were just introduced, the setting that everyone was asked to use was Edge because no PCI device back then supported IRQ sharing. However, now that almost every PCI device supports IRQ sharing and IRQs are usually in shortage, it's best to set it as Level so that your PCI devices can share IRQs. So, set it to Level unless you are using old edge-triggered PCI cards.

PIRQ_0 Use IRQ No. ~ PIRQ_3 Use IRQ No.

Options : Auto, 3, 4, 5, 7, 9, 10, 11, 12, 14, 15

This feature allows you to manually set the IRQ for a particular device installed on the AGP and PCI bus. This is especially useful when you are transferring a hard disk from one computer to another; and you don't want to reinstall your OS to redetect the IRQ settings. So, by specifying the IRQ for the devices to fit the original settings, you can circumvent a lot of configuration problems after installing the hard disk in a new system.

Notes :-

• If you specify a particular IRQ here, you can't specify the same IRQ for the ISA bus. If you do, you will cause a hardware conflict.
• Each PCI slot is capable of activating up to 4 interrupts - INT A, INT B, INT C and INT D
• The AGP slot is capable of activating up to 2 interrupts - INT A and INT B
• Normally, each slot is allocated INT A. The other interrupts are there as reserves in case the PCI/AGP device requires more than one IRQ or if the IRQ requested has been used up.
• The AGP slot and PCI slot #1 share the same IRQs
• PCI slot #4 and #5 share the same IRQs
• USB uses PIRQ_4

Below is a table showing the relations between PIRQ and INT :-

You will notice that the interrupts are staggered so that conflicts do not happen easily. Still, because the AGP slot and PCI slot 1 share the same set of IRQs, it's best to only use either one of those two slots unless you don't have other slots to use. The same goes for PCI slot 4 and 5.

Normally, you should just leave it as AUTO. But if you need to assign a particular IRQ to a device on the AGP or PCI bus, here's how you can make use of this BIOS feature. First of all, check out which slot the device is located in. Then, check the table above to determine which is its primary PIRQ. For example, if you have a PCI network card in PCI slot 3, the table shows that its primary PIRQ is PIRQ_2 because all slots are first allocated INT A if possible.

After that, select the IRQ you want to use for that slot by assigning it to the appropriate PIRQ. If the network card (in the example above) requires IRQ 7, then set PIRQ_2 to use IRQ 7. The BIOS will then allocate IRQ 7 to PCI slot 3. It's that easy! :)

Just remember that the BIOS will try to allocate the PIRQ linked to INT A for each slot. So, the AGP slot's and PCI slot 1's primary PIRQ is PIRQ_0 while PCI slot 2's primary PIRQ is PIRQ_1 and so on. It's just a matter of linking the IRQ you want to the correct PIRQ for that slot.

Note that the Intel i8xx chipsets have 8 interrupt lines (INT-A to INT-H). So, the AGP slot will always have its own IRQ in motherboards using the Intel i8xx chipsets. Thanks to alex-the-cat for that info! :)