PNP OS Installed

Common Options : Yes, No

Quick Review

What this BIOS feature actually does is determine what devices are configured by the BIOS when the computer boots up and what are left to the operating system.

Non-ACPI BIOSes are found in older motherboards that do not support the new ACPI (Advanced Configuration and Power Interface) initiative. With such a BIOS, setting the PNP OS Installed feature to No allows the BIOS to configure all devices under the assumption that the operating system cannot do so. Therefore, all hardware settings are fixed by the BIOS at boot up and will not be changed by the operating system.

On the other hand, if you set the feature to Yes, the BIOS will only configure critical devices that are required to boot up the system. The other devices are then configured by the operating system. This allows the operating system some flexibility in shuffling system resources like IRQs and IO ports to avoid conflicts. It also gives you some degree of freedom when you want to manually assign system resources.

Of course, all current motherboards now ship with the new ACPI BIOS. If you are using an ACPI-compliant operating system (i.e. Windows 98 and above) with an ACPI BIOS, then this PNP OS Installed feature is no longer relevant. This is because the operating system will use the ACPI BIOS interface to configure all devices as well as retrieve system information.

But if your operating system does not support ACPI, then the BIOS will fall back to PNP mode. In this situation, consider the BIOS as you would a Non-ACPI BIOS. If there is no need to configure any hardware manually, it is again recommended that you set this feature to No.

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.

Britt Turnbull recommends disabling this feature if you are running the OS/2 operating system, especially in a multi-boot system. This is because booting another operating system can update the BIOS which may later cause problems when you boot up OS/2.

To sum it all up, except for certain cases, it is highly recommended that you to set this BIOS feature to No, irrespective of the operating system you actually use. Exceptions to this would be the inability of the BIOS to configure the devices properly in PnP mode and a specific need to manually configure one or more of the devices.