John Payson wrote:

> IBM in their infinite wisdom decided to have the interrupts
> on the PC be active high.  Thus, the simplest way of making
> a driver that can share the line is to use a 3-state buffer
> chip whose input is always high; the enable on the buffer
> then switches the output between floating and high.

  That's true, but *not* what was implemented.

>> My understanding is that no one implemented shared interrupt drivers
>> because the hardware was essentially broken...

  I agree, that is the long and short of it.

> In another piece of their infinite wisdom, IBM decided to
> make interrupts edge-triggered rather than level-controlled.

  If my previous comments were to convey the impression that the PC
design was, and parts of it remain, anything other than an overall
balls-up, then please forgive me.
--
  Cheers,
        Paul B.