AGP slot and PCI slot #1 always share same IRQ# no matter what? Please explain

[Londog007]

Have a Acer 6120 pent 400 mhz W98 SE. With a AGP slot,3 PCI slots, and 1 ISA slot on the bottom. THE
TNT2 ultra is in AGP slot with IRQ 9. Anything I put in PCI slot 1(underneath AGP slot) takes IRQ 9 too, Even
with IRQ 3,4,and 5 free??? Are these 2 slots tied together in some way. Trying to fit PCI Sound Blaster Live,
PCI DSL INTEL Modem and Voodoo2 in computer. Unfortunatly Voodoo2 only fits in bottom PCI slot number3.
Or I could put it in PCI slot 1 since Voodoo2 does not use a IRQ number. USWEST or QWEST says thier
modem needs
its own IRQ number??? And I heard Sound Blaster Live needs its own IRQ number and should not be in PCI slot
below AGP??? I also heard try not to put anything in the bottom PCI slot number 3??? I guess my question is if
its possible for the AGP slot and PCI slot number 1 to assign them different IRQs??? AND if The AGP TNT2
Ultra and the INTEL DSL modem can handle sharing IRQ 9 with out any slow down or giving me extra lag when
playing demanding online games like Rogue Spear! If someone could educate me on this it would be most
appreciated. Studying for A+ and it doesnt go this
deep. Thanks

 

[Mark R]

The PCI bus (including AGP slot) is limited to 4 IRQs. Most mobo designers hardwire their boards so that PCI 1 shares an IRQ with AGP. So, while on your system, IRQs 3, 4 and 5 are free, they cannot be used by your modem, etc. because those IRQs have not been allocated to the PCI bus.

IRQ sharing is not a problem - PCI cards are required to be able to share IRQs.

The SB Live! doesn't need its own IRQ, but evidence from these forums and others suggests that it does seem to suffer from some serious bugs if it does try to share. The SB live is the only card that I've heard of that has problems sharing IRQs. I doubt that your modem has any problems with it.

If you are really paranoid about IRQ sharing then put the voodoo2 next to AGP, then SB live then modem.

The point is this, if your system boots, and all the cards appear to work, then the IRQs are not a problem. People get so worked up over IRQ sharing, but plug and play does work, and works very well - so that the settings it comes up with work virtually every time.

 

[MIDIman]

ditto...though network cards require an IRQ to work properly.

I've ripped out my hair having this problem with a network card that would always share itself with the AGP. I took the time to go through the entire System list, one by one, and notate which IRQs were going to what part. I then moved the card to another slot (it was in Slot1) and found that everything could be taken care of by disabling PnP in BIOS, and manually setting IRQs in the PCIlist of BIOS - I used all the same assigned IRQs I notated before, except made sure the network card was set to a free IRQ that was different from the AGP slot.

 

[Mark R]

What type of network card was this? I'd like to avoid it in the future.

I've used about 8 different brands of PCI network cards, from Intel and 3Com all the way down to the cheap no-name ones. I have never had one fail to work correctly because of IRQs, on any of my computers, from 486 to Pentium 2 (both FX and BX chipsets).

In fact, I have never had any PCI/AGP card fail to work because of IRQs - although, I will admit that I've never used an SB Live!

 

[superbaby]

I've had a really really really cheapass 10BaseT that would NOT work if it was seated next to another NIC.

Probably should go buy a decent 10/100... sigh too lazy.

 

[Theraven]

Actually, you need to reserve an IRQ for the sound blaster emulation. Go in the Bios and reserve the IRQ 5 for legacy support. By default, your bios assigns all IRQ to PCI slots but the sound blaster live needs 2 IRQ, one for the card itself and one for the emulation. (Can't explain how it works but that's the way it is. There should not be a problem since the Sound Blaster Live is PNP but if you do have IRQ conflicts with that card, have the IRQ 5 reserved for it.

 

[Nih]

I believe the reasoning is that if you are using agp , you don't use slot 1, If you use pci vga, you use the first pci slot and not the agp, Mind you the Tyan trinity 400 agp and pci #2 are shared , which kinda throws a wonk into things. I would suggest you enable acpi and see if your system runs stabily with both agp and pci#1 populated

 

[Nih]

Oh another thing, If you share an Acer aln-201 nic on an a7v with the mass storage controller,, no worky!!!

 

[Londog007]

Thanks everyone for replys,Voodoo2 only fits in bottom in bottom slot unfortunatly, so I took it out. USWEST still claims thier DSL modem needs its own IRQ. SO I have SB Live in PCI slot2(IRQ 5 with SB 16 Emulation disabled) and DSL Intel com modem in slot PCI slot(IRQ 10).PCI slot 1 empty. OH on my Acer I can not disable PNP in Bios,thier is no option, I checked with manufacture. Thanks again.