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Isnt it 16 IRQ's?

April 30, 2007 at 12:04:49
Specs: WinXP Pro, Dual PIII500

I had some spare time to play around. So I cloned my XP drive and booted it. Then changed the HAL to MPS Multiprocessor rather than ACPI Multiprocessor.

Now that XP is using MPS it responds to BIOS changes. So I change from MPS version 1.1 to 1.4 in BIOS.

In XP it seems all the devices are now on their own IRQ (which is good) but with numbers going up to 128! I thought there were only 16 of them? Are they virtual IRQ's or something?

Bill


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#1
April 30, 2007 at 12:11:00

In Windows, it isn't virtual - it's Shared IRQs.

http://www.helpwithpcs.com/upgradin...

BE WARNED:

Don't ever tweak with the IRQs because Windows like to have complete control. Otherwise Windows will bite you back like a "..Woman Scorned" (quoted the good ole Shakespeare)

i_XpUser


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#2
April 30, 2007 at 12:45:34

How are the IRQs shared when they have individual numbers? With ACPI they used to have about 4 devices all sharing one IRQ.

ie on MPS HAL XP:

IRQ - Device

26 - Win2003 Promise Ultra133 TX2
36 - ALi PCI to USB Open Host Controller
37 - USB Root Hub
128 - Matrox Millenium G550

Bill


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#3
April 30, 2007 at 12:50:28

<sighs> THIS is why .. says Windows as the woman about to be scorned.

i_XpUser


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Related Solutions

#4
April 30, 2007 at 14:46:51

XPUser

I don't know the answer but in fairness to the poster he didn't say he was monkeying around with IRQ's, has none that "appear" to be sharing (no duplicate numbers) and is only querying why they go up beyond 16.

There might well be some misconceptions but just the same I don't really see an answer in that provided so far, so the <sighs> crack is a bit unkind. Posters come here for advice so they cannot necessarily be expected to know all about IRQ's.

DerekW


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#5
April 30, 2007 at 21:04:21

Except for a couple of points. We all have google or other search engines which if used will educate the user. I suspect the sigh was from pointing Bassquake in that direction.

Might mention the post is hardware so for a discussion about irqs that would have been a better place for the post. the irq behaviour isn't unique to xp.


Are you ready for where Microsoft wants you to go today?


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#6
April 30, 2007 at 22:55:31

"the irq behaviour isn't unique to xp."

That's right. Just take a look at the IRQ assignments under Linux. Graphics card is usually on IRQ-128.

Please let us know if you found someone's advice to be helpful.


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#7
May 1, 2007 at 01:02:18

AFAIK the BIOS only has 16 IRQ's, by turning of P'n'P in BIOS this lets the O/S assign IRQ's numbering, which has no relation to BIOS IRQ's, it is an ACPI workaround.....SIB

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#8
May 1, 2007 at 08:10:22

@wanderer: Ur right, I should have posted in hardware, though I thought irq was windows only.

@Sci-Guy: Interesting that Linux graphics card uses 128. Same as on my XP when using MPS hal.

@Santa: "by turning of P'n'P in BIOS this lets the O/S assign IRQ's numbering, which has no relation to BIOS IRQ's, it is an ACPI workaround." Does it apply to MPS as well?

Bill


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