IRQ Question on Gigabyte 7VRXP

[Hittman]

I just noticed today that my Gigabyte 7VRXP is claiming to have 129 IRQs under Device Manager in Windows XP Professional. The IRQs start with the System Timer on 0 and the last device is my Radeon 8500 on IRQ 128. I really like the idea of having this many IRQs, but how is this possible?

 

[ssanches]

That's the WinXP ACPI HAL. The system can set those higher IRQ's provided your PC is a WinXP ACPI compliant system. Those IRQ's are virtualised

 

[AndyHui]

Most of the very latest motherboards implement support in the chipset and the BIOS for an IO-APIC: the Input/Output Asynchronous Programmable Interrupt Controller.

It gets past the old 16 IRQ limitation by using a bus to address the IRQs. Depending on the implementation you can get anything from 24 to 255 hardware IRQs. In the past, you only saw this on multi-processor systems, but lately it's been starting to show up on uniprocessor systems as well. Only Windows 2000 and Windows XP's ACPI HAL have the ability to address these additional IRQs.

 

[Hittman]

Thanks. I have built some systems using SuperMicro dual processor boards that had 32 IRQs, but I had never seen anything like this in the past.