BIOS Settings - PCI / PnP Configuration



The settings in this section deal specifically with the PCI bus 
and Plug and Play (PnP) settings. PCs that do not have a PCI bus 
will of course not have this section at all; older buses such as 
the VLB did not have the features that this section of settings 
controls. The PCI bus for the most part takes care of itself, 
but the settings in this section can be used when particular 
behavior by the bus or expansion cards needs to be 
addressed.

	Warning: This section contains many advanced settings 
that in the vast majority of cases you do not need to change. 
For most users, using some form of the provided automatic 
configuration setting is highly recommended.


Plug and Play Aware OS

This setting is shown on only some BIOSes. If present, enabling 
this tells the BIOS that you are using an operating system that 
supports the Plug and Play specification (such as Windows 95). 
When enabled, the BIOS will look for and initialize any Plug and 
Play cards in the system. Enable the setting if using Windows 95 
or another Plug and Play compatible OS. The default is normally 
"Disabled".

	Note: Some BIOSes will perform the initialization of 
Plug and Play cards automatically regardless of the operating 
system being used, and will thus not have this setting. Some will 
work fine with Plug and Play regardless of how this option is 
set. However, on some systems that have this setting, Plug and 
Play may not function properly if the setting is disabled.


PCI IDE Bus Master

Some BIOSes have an explicit setting to enable bus mastering of 
PCI IDE hard disk drives. If this setting is present in your 
BIOS and you are using PCI IDE bus mastering you should set 
this to "Enabled". Otherwise it should be left on the default, 
which is "Disabled". 


Automatic Resource Allocation

There are several settings in the PCI / PnP Configuration 
section of the BIOS program that deal with assigning interrupt 
resources. This includes both regular IRQs and the internal PCI 
interrupt resources. For most applications there is no need to 
manually select or deal with these resources; in this case the 
default setting of "Auto" should be selected, to enable 
automatic resource allocation. Not all BIOSes have this setting.

When you use the "Auto" setting the BIOS will normally "lock" 
the "PCI IRQ and DMA Settings" (below) to reflect the fact that 
they are being set automatically by the BIOS. To unlock the 
individual settings so you can change them, you must turn off 
the "Auto" setting.


PCI IRQ and DMA Settings / IRQ <n> Assigned To / DMA <n> 
Assigned To

When automatic resource allocation is not used, the BIOS allows 
you to specifically designate which system interrupts (IRQs) and 
direct memory access channels (DMAs) you want it to be able to 
use for setting up Plug and Play devices. For each IRQ or DMA, 
except ones reserved by the system, you can designate either 
"PCI/PnP" or "ISA/Legacy". When a resource is assigned to 
"ISA/Legacy" it is declared "off limits" to the BIOS. 

The IRQs that you can normally set here are IRQs 3, 4, 5, 7, 9, 
10, 11, 12, 14 and 15. The DMA channels are 0, 1, 3, 5, 6 and 7. 
(The others are reserved by system devices.) The default on most 
systems for each of these settings is "PCI/PnP". If your system 
does not have automatic resource allocation (which is preferred) 
then it is usually best to leave these settings on "PCI/PnP" 
unless you are having a problem with Plug and Play. For example, 
if PnP keeps taking a resource for a PnP card that you need for 
an ISA card, you might want to set that resource to "ISA/Legacy" 
here to reserve it.

	Note: If automatic resource allocation is enabled, these 
options will normally either be locked to prevent change, or even 
cleared from the screen altogether, since the BIOS will control 
them automatically.


1st / 2nd / 3rd / 4th Available PCI Interrupt

The PCI bus uses its own internal interrupts , usually numbered 
#1 to #4 or #A to #D. Some PCI cards need to be able to use one 
of the regular system IRQs (interrupt request lines) to 
communicate with the processor. This setting "maps" the PCI 
interrupts to regular system IRQs by telling the BIOS which 
regular interrupt line to use for PCI cards that need one. The 
usual choices for this are IRQ9, IRQ10, IRQ11 and IRQ12.

	Note: If automatic resource allocation is enabled, these 
options will normally either be locked to prevent change, or even 
cleared from the screen altogether, since the BIOS will control 
them automatically.


PCI VGA Palette Snoop

The VGA "palette" is the set of colors that are in use by the 
video card when it is in 256-color mode. Since there are 
thousands of colors and only 256 can be used in that mode, a 
palette containing the current colors is used . Some special VGA 
cards, high-end hardware MPEG decoders etc. need to be able to 
look at the video card's VGA palette to determine what colors are 
currently in use. Enabling this feature turns on this 
palette "snoop".

This option is only very rarely needed. It should be left at 
"Disabled" unless a video device specifically requires the 
setting enabled upon installation.
