Path: utzoo!utgpu!news-server.csri.toronto.edu!helios.physics.utoronto.ca!ists!yunexus!rreiner
From: rreiner@yunexus.YorkU.CA (Richard Reiner)
Newsgroups: comp.sys.ibm.pc.hardware
Subject: IRQ 2 on AT-class machines
Message-ID: <22603@yunexus.YorkU.CA>
Date: 30 Apr 91 17:23:33 GMT
Organization: York U. Computing Services
Lines: 18

I've seen the documentation for several cards claim that IRQ 2 must
not be used for expansion cards on AT-class machines, as it is
reserved for something or other (they never say what).

However, all the reference works I have on hand (including one of the
Norton books, Ralf Brown's interrupt list, and some motherboard
reference guides) indicate that the only use of IRQ2 (which is really
remapped to IRQ 9 on the AT bus, since the real IRQ 2 is used for the
cascade between the PICs) in AT-class machines is for VGA and EGA
cards to indicate sync, a feature which is almost never used and which
is disabled by default on almost all VGAs and EGAs, thus leaving IRQ 9
free.

So what's the truth here?  

Thanks,

//richard