IRQ conflict on SCO Open Desktop

Dick Dunn rcd at
Wed May 30 11:09:46 AEST 1990

davidsen at sixhub.UUCP (Wm E. Davidsen Jr) writes:
> wul at writes:

> | Yes.  The standard configuration for network cards used internally
> | with TCP/IP (3c501s, 3c503s, WD8003s) is IRQ2.
>   Right on! This buys you one more interrupt than many of the other UNIX
> versions support.

Huh?  Which UNIX versions don't support this?  I think it's just a
nomenclature problem.

A device which generates IRQ2 on a PC bus generates IRQ9 on an AT bus.
They go to the same line on the card-edge bus connector.

You cannot generate an IRQ2 on an AT bus.  There's no line on the bus for
it, since it's used internally for the second interrupt controller.

Some instructions call it IRQ2, since that makes it easier to understand
how you use a PCish card in an ATish machine.  They either let you say "2"
and know you mean "9"--in which case they may or may not also recognize
"9"--or they make you say "9" when you think you mean "2".  (It's sort of
like saying "dog kennel" when you mean "mattress".:-)  But you can't put
something on both 2 and 9.

This is an admittedly confusing issue; it should be in the list of
frequently questioned answers.
Dick Dunn     rcd at    uucp: {ncar,nbires}!ico!rcd     (303)449-2870
   ...Simpler is better.

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