Tweaking Optimizing Windows.pdf - GEGeek

To sum it all up, APIC provides multiprocessor support, more IRQs and faster interrupt handling which are not possible with the old
8259 PIC. Although they can be used in single-processor boards, you are more likely to find them in multi-processor motherboards.
This is because APIC is only supported in Windows NT, 2000 and XP. It is not supported in operating systems that are required to
support MS-DOS device drivers, i.e. Windows 95/98. But as users transition to Windows XP, you can expect more manufacturers to
ship single-processor boards with I/O APICs.
If your single-processor motherboard supports APIC and you are using a Win32 operating system (Windows NT, 2000 and XP),
it's recommended that you enable this feature to allow faster and better IRQ handling. If you are using a multiprocessor
motherboard, you must enable this feature because it's required for IRQ handling in multiprocessor systems.
However, if you are running Windows 95/98 or a DOS-based operating system on a single-processor motherboard, you
must disable this feature. This is because MS-DOS drivers assume they can write directly to the 8259 PIC (APIC did not exist yet
in those days!) and its associated IDT entries. Disabling this feature forces the APIC to revert to the legacy 8259 PIC mode.
Assign IRQ for USB
This BIOS feature is somewhat similar to Onboard USB Controller. It enables or disables the motherboard's onboard USB controller
by determining whether it should be assigned an IRQ. Enable this feature if you want to attach your USB devices to the onboard
USB controller.
If you disable this feature, the USB controller will not be assigned an IRQ. This disables the controller and therefore you won't be
able to connect any USB devices to it. But if you don't use any USB devices, this frees up an IRQ for other devices to use. This is
particularly useful when you have many devices that can't share IRQs. Disabling this feature may not be necessary with APICcapable
motherboards because they come with more IRQs.
Assign IRQ for VGA
Many graphic cards require an IRQ to function properly. Disabling IRQ assignment for such cards will cause improper operation
and/or poor performance. Therefore, it is recommended that you enable this feature. Doing so allows the BIOS to assign an IRQ to
the graphics card. Some graphics cards may not need an IRQ to work. These cards are usually the low-end cards that provide basic
video functions. Check your graphics card's documentation to confirm if it requires an IRQ to work.
If your graphics card doesn't require an IRQ, then you can disable this feature to release an IRQ for other devices to use. This is
particularly useful when you have many devices that can't share IRQs. Disabling this feature may not be necessary with APICcapable
motherboards because they come with more IRQs. When in doubt, it's often best to leave it enabled as graphics cards
generally function better with an IRQ. This is true even for cards that don't require IRQs.
Force update ESCD
The ESCD (Extended System Configuration Data) is a feature of the Plug and Play BIOS that stores the IRQ, DMA, I/O and memory
configurations of all ISA, PCI and AGP cards in the system (Plug and Play-capable or otherwise). The data is stored in a special area
of the BIOS ROM so that the BIOS can reuse the configuration data when it boots up the system. As long as there are no hardware
changes, the BIOS does not need to reconfigure the ESCD.
If you install a new piece of hardware or modify your computer's hardware configuration, the BIOS will automatically detect the
changes and reconfigure the ESCD. Therefore, there's no need to manually force the BIOS to reconfigure the ESCD. However,
sometimes, the BIOS may not be able to detect the hardware changes and the a serious conflict of resources may occur. The
operating system may not even boot as a result. This is where the Force Update ESCD BIOS feature comes in.
This feature allows you to manually force the BIOS to clear the previously saved ESCD data and reconfigure the settings. Just
enable the feature and reboot your computer. The new ESCD should resolve the conflicts and allow the operating system to load
normally. There's no need for you to manually disable this feature yourself as the BIOS will automatically reset it to the default
setting of Disabled after reconfiguring the ESCD.
PIRQ x Use IRQ No.
This feature allows you to manually set the IRQ for a particular device installed on the AGP and PCI buses. This is especially useful
when you are transferring a hard disk from one computer to another; and you don't want to reinstall your operating system to
redetect the IRQ settings. 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. However, this is only required for non-ACPI systems.
Notes (these may differ from motherboard to motherboard) :-
- 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 IRQ.
- PCI slot #4 and #5 share the same IRQs.
- USB uses PIRQ_4.
Below is a table showing the relations between PIRQ and INT in the reference motherboard :-
Signals AGP Slot PCI Slot 1 PCI Slot 2 PCI Slot 3 PCI Slot 4 PCI Slot 5
PIRQ_0 INT A INT D INT C INT B
PIRQ_1 INT B INT A INT D INT C
PIRQ_2 INT C INT B INT A INT D
PIRQ_3 INT D INT C INT B INT A