28 Nov
2007
28 Nov
'07
10:18 p.m.
On Tuesday 27 November 2007 17:22, Tony Duell wrote:
Hm. Remembering an XT-type MB I had (maybe still have?) that someone had put
black electrical tape over the top of one of the slot connectors, and if
that was maybe slot 8, and wondering if I still have that board, maybe...
--
Member of the toughest, meanest, deadliest, most unrelenting -- and
ablest -- form of life in this section of space, ?a critter that can
be killed but can't be tamed. ?--Robert A. Heinlein, "The Puppet Masters"
-
Information is more dangerous than cannon to a society ruled by lies. --James
M Dakin
What was
special about slot 8?
In a true-blue IBM PC/XT (5160) or PortablePC (5155), and AFAIK very few,
if any clones, the data bus on slot 8 is wired to the opposite side of a
bus buffer to the data bus to the other 7 sltos. For that reason, the card
in slot 8 has to assert (pull low) one pin on the conenctor on read cycles
to that board (I forget the exact pin, I can look it up if you need it).
The IBM Async card (RS232 card) was one card that could do this (jumper
selected). I have heard that one reason such a card was included with
every PC/XT was that it was bout the only thing that could go in slot 8,
and by putting it there at the factory it avoided too many calls from
customers 'Why doesn't the XYZ card work properly in my new XT?'