I often read advice to folks troubleshooting PC problems to check if they have devices sharing IRQs, and to move cards to different PCI slots to avoid IRQ sharing. Is this usually good advice, and, if so, why are PCs designed designed to share IRQs in the first place? What exactly is an IRQ (Interrupt Request?) and will they be phased out soon? How can I get a list of my current IRQ assignements under XP? Is this an OS-dependent thing or does MacOS and Linux include these things too?
An IRQ is an interrupt. This is basically you card telling the processor that it has something that the processor should do.
An example would be the mouse controller would send and interrupt telling the processor that a button has been pressed or that the mouse has moved.
I don’t think that interrupts will ever go away. What is happening is that cards and software are getting better at ensuring that each card uses interrupts with out conflicts. So that you, the end user, do not have to worry about these things.
Macs have interrupts that are used in basically the same way though I am sure that the specifics are different. Macs have less problems with this sort of thing mainly because Apple controls the hardware in a way that nobody controls the hardware for PCs. The Apple ensures that things work without conflict.
Linux on PC hardware has exactly the same IRQ stuff as the PC with windows.
IRQs are with us. They are not a bad thing, except that, like other factors that hobble the PC, is a legacy from decades ago.
Interrupts are signals. What they do is to tell the computer - more specifically, the CPU - something wants its attention. The advantage of having interrupts is the CPU can do its own thing instead of hanging around waiting for something to happen, say, the graphics card wants some more data.
Unfortunately, when the PC was first designed, it was decided that 9 hardware interrupts (IRQs) were sufficient even though the 8088, ancient as it was, was capable of having 255. Later, the range was expanded to 15 IRQs, but that can prove to be insufficient for a fully loaded PC.