I thought only some EGA cards at one time had actual IRQ's and even then I don't think the irq is enabled by default.
If there's multiple things using the same irq but they aren't operating at the same time, it should probably work fine.

I see, I didn't find any IRQ informaiton on the card so I thought it doesnt use it (still dont quite understand what IRQ is fully).
I red that only IRQ 0 and 1 are used in XT systems, is this correct?

This seems to give a decent enough explanation

http://en.wikipedia.org/wiki/Interrupt_reques … architecture%29

The card triggers the irq line in the isa bus, this triggers the interrupt controller to signal the processor to generate an interrupt.
It all depends on whatever software is listening on that interrupt what's gonna happen afterwards.
Starting some soundblaster playback application, it'll hook the right interrupt, start the soundblaster and wait for the card to generate the IRQ and subsequent interrupt

On a bare XT without any extra IO cards or onboard IO I'd guess IRQ 0 and 1 are the only ones in use yes. just hardwired on the motherboard.

IRQ stands for Interrupt Request.
An interrupt is a signal that hardware can send to well, interrupt the CPU, so that it can process the request from the hardware (such as incoming data, or signaling that a certain operation is complete or such).
Regular PC videocards don't use interrupts. All communication is driven by the CPU. If the CPU needs to wait for the videocard to be in a certain state, it will poll the videocard registers.

Here is a list: en.wikipedia.org/wiki/Interrupt_request ... hitecture)
In theory you are right... the minimum configuration for an IBM PC/XT compatible would be to only have some memory (IRQ0) and a keyboard (IRQ1).
Most systems have a floppy controller as well, which will use IRQ6. And it is also common to have a COM port and/or an LPT port, so IRQ4 and IRQ7 are often used as well.

If i recall correctly IBM's EGA card uses IRQ2, as does its VGA card.

Scali wrote:

Regular PC videocards don't use interrupts. All communication is driven by the CPU. If the CPU needs to wait for the videocard to be in a certain state, it will poll the videocard registers.

Well that really depends. Some cards, like the S3 Vision 928 based Spea Mercury requires to have IRQ enabled such that Windows DCI acceleration works. Also PCI cards and newer use by default an IRQ.

Stojke wrote:

Which IRQ is occupied by the VGA card? In my Philips NMS 9100 I have disabled everything onboard (except CGA, it seems it can no […]
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Which IRQ is occupied by the VGA card?
In my Philips NMS 9100 I have disabled everything onboard (except CGA, it seems it can not be disabled) and plan on using some expansion cards.

The hard card can be set to IRQ2/5 , but I remember that IRQ 2 is used by VGA. If I occupy IRQ5 with the hard card I would need to change the Sound Blaster IRQ.
Is it possible to set the VGA card to lets say 3? The VGA card is Video 7 VEGA VGA 256kB.

Is better for the sound blaster to use the IRQ 7 instead of IRQ 5, because some games cant auto detect the soundblaster if its using the IRQ5..
For the first time i made the same fault.. Later i changed the SB IRQ to 7..

I dont think the graphic cards (ISA) would use an IRQ, but i know it shadows its roms the the upper memory location.

elianda wrote:

Well that really depends. Some cards, like the S3 Vision 928 based Spea Mercury requires to have IRQ enabled such that Windows DCI acceleration works. Also PCI cards and newer use by default an IRQ.

With "regular PC videocards" I meant the classic MDA/Hercules/CGA/EGA/VGA (the original IBM/Hercules standards basically), implying ISA.
Newer SVGA cards may have interrupt support for things like vsync and special acceleration features... and PCI cards are a different story altogether anyway, since they support bus mastering DMA and whatnot.

IRQ 2:
http://www.osdever.net/tutorials/view/irqs

Thanks all for clarifying how IRQ works! Now i understand fully 😀
And i have set Sound Blaste rto IRQ7. Only thing left is to get the floppy to work.

Stojke wrote:

And i have set Sound Blaster to IRQ7.

Yes, that was the default on early Sound Blasters. As you can see, this is shared with LPT1, but normally that isn't a problem.
Later Sound Blasters were configured to IRQ5 by default though, which is shared with LPT2, which most people don't have anyway. Perhaps to avoid issues with some computers/software.
I would recommend IRQ7, since I have found a few games/demos that have the IRQ hardcoded, so they won't work.
Same with base address 220h. This is the default address, and is hardcoded in some software.