8 Nov
2006
8 Nov
'06
4:42 p.m.
--- Tony Duell <ard at p850ug1.demon.co.uk> wrote:
I read something in an early BYTE stating that as
time went on, the dip switches on the pc's mobo had
little consequence on the systems ability to determine
the amount of ram installed. Am I in error to state
that the dip switches are read by code? Perhaps
someone can confirm, deny, elaborate, denounce...
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I have an
original XT board with 256k on it and I
want to take it up to
640k total.
If it's an IBM XT mainboard, there's an easy way to
do this (and not use
up any expansion slots).
Put 41256 chips in banks 0 and 1, and 4164s in banks
2 and 3 on the
mainboard. Put a 74S158 (or 74F158) multiplexer chip
in the emptu socket
at the front right, pointing the same way as the
chips around it. Set the
DIP switches for 256K RAM, and solder a jumper wire
between pads E1 and E2.
That's it. You have a 640K XT mainboard.
-tony