Why there are different IRQs in BIOS and OS? (and which to believe when assembling)

[Nowhere]

I'm reinstalling OS on my computer...thought this time I might do this "properly". That also means: trying not to have devices that share IRQs (especially devices like Radeon 8500, or TV card).
But...why I see different things in BIOS and in OS? Which one is the better criterion?
(and even the ones in BIOS change after I select "emulate legacy USB devices", but I'm unable to check how this influences setting in Windows)

[DJ]

AFAIK from wink2k onward the OS uses ACPI to manage all these resources automatically. You no longer have the limited IRQs that win98 had. Its best to just leave as is. As long as you are using ACPI your manual bios settings will be overridden.

[Nowhere]

OK...but does this really mean that sharing of IRQs can be totally ignored now? Especially since I have GFX card which, I believe, was described by Gurm as "fireworks"...and which shares IRQ with souncard (and...there are symptoms that can suggest that's a problem)

(and I can only change BIOS IRQs by moving cards to different slots...)

[DJ]

Generally the mobo manual will tell you which slots share IRQs. You can try a different slot as you suggested. Alternatively you can change from ACPI to standard PC in the device manager but then you will probably have to manage all IRQs and I don't think you would like that. With ACPI many things can share the same IRQ and it should still work, but sometimes it doesn't.

[Admiral]

Generally if you have a Creative sound card it's best not to share IRQ with anything (safe maybe USB controller)

[Nowhere]

...or Radeon 8500? (so I've heard...)

maybe I'll write down cards I have, would be great if you knew how each of them behaves...

AGP:
- Radeon 8500 64MB (made by Pinnacle, similar to All-in-wonder but without TV; only in&out and Firewire (by Agere, which also has its own IRQ, the same as card AFAI see))

PCI:
- Matrox G450 16MB PCI
- Intel PRO/1000 MT Dual Port server adapter (and this one's a bit tricky - has PCI-X so it won't fit in every PCI slot due to "things" on the mobo; might throw in 3com 3c905c-tx-m instead)
- Leadtek TV card on Brooktree chip, BT878
- Aureal Vortex SQ2500 (so no Creative...but I'm tempted to sin and buy Audigy2 )

[Jon P. Inghram]

Check that APIC is turned on in the BIOS if it's there, that's what gives you the extra interrupts.

[DJ]

...or Radeon 8500? (so I've heard...)

maybe I'll write down cards I have, would be great if you knew how each of them behaves...

AGP:
- Radeon 8500 64MB (made by Pinnacle, similar to All-in-wonder but without TV; only in&out and Firewire (by Agere, which also has its own IRQ, the same as card AFAI see))

PCI:
- Matrox G450 16MB PCI
- Intel PRO/1000 MT Dual Port server adapter (and this one's a bit tricky - has PCI-X so it won't fit in every PCI slot due to "things" on the mobo; might throw in 3com 3c905c-tx-m instead)
- Leadtek TV card on Brooktree chip, BT878
- Aureal Vortex SQ2500 (so no Creative...but I'm tempted to sin and buy Audigy2 )

Looks like you are ovedue for an upgrade!

[The PIT]

Generally if you have a Creative sound card it's best not to share IRQ with anything (safe maybe USB controller)

Only if it's a Via chipset

[Nowhere]

Looks like you are ovedue for an upgrade!

Uhmm...why do you think so from those specs? I can easily pick up motherboard with AGP for any Core 2 Duo or Athlon AM2
Ok, ok, I have AthlonXP 1700+...which _must_ be enough (and basically it is). Anyway recently I play mostly Diablo2...
(and do I really have to mention pluses of Intel server NIC, Brooktree chip on TV card and A3D in...D2 for example? )

Only if it's a Via chipset

At least this part is easy - it isn't (popular here long time ago SiS, 746FX in this case)

[Nowhere]

Allright, at first it seemed that IRQ assigments in BIOS are almost chaotic; after a while I came to conclusion that not only AGP shares IRQ with PCI4, but I identified two PCI slots which almost always share IRQ (even if it changes) and two which _sometimes_ share it.

I decided to put network card and Vortex soundcard in shared slots, and now Radeon, Matrox G450 and TV card have their own IRQ both in BIOS and OS (even though in both places they differ, but there is some relation between them definatelly). I figured those three cards have greater need for their own IRQ than network and sound card...

One less _possible_ cause of problems...

Thanks for help/participation in brainstorming

PS. Jon P. Inghram, BIOS in Asrock boards is a bit...too minimalistic to do that