What is ACPI and what does it do for me?

[GNEP]

Hmmm... all very interesting...

[Ribbit]

Originally posted by Drizzt
Just to add a bit of mis-information (hope the term is correct): PIC was capable to address up to 256 IRQs.
APIC a lot more, I don't remember how much exactly.

(Wombat, you are the tecnician and I'm too old to remember the answer: why the hell with 256 IRQs available, old DOS gave us only 16? Are the other secretly used by the motherboard, or is still because no one will never need more than 640kbyte? )

WARNING: the following is almost certainly misinformation based on my imperfect memory...

It's actually the processor which has 256 'interrupts'. Some are used for I/O interrupts, some are used internally (e.g. illegal instruction exceptions), and the rest can be hooked to software for whatever reason (remember how DOS TSRs worked by hooking interrupts?) and called with the INT instruction.

The 8259 PIC as used in PCs can handle 8 interrupts. You get 16 in the AT and above because there are two PICs chained together (that's why interrupts 2 and 9 were/are the same - the second PIC is connected to interrupt 2 on the first).

Clear as mud?

[Wombat]

Be careful not to confuse hardware interrupts with software interrupts. They function much the same way as far as the CPU is concerned, but their origins are very different, as Ribbit laid out.

[Gurm]

Bingo. The CPU has 255 soft "interrupts", but there are only 16 IRQ's (Interrupt ReQuest Lines) in the hardware, provided by twin 8-IRQ PICS.

I should have made clear that I was referring to ACPI+APIC, which only now are video editing and pro-audio manufacturers getting around to fully supporting. There were, and in some cases still are, very good reasons to run in Standard PC mode.

I simply wanted to make it clear that "because it'll run mega-hyper faster d00D!" is not one of them.

- Gurm