8 Nov
2006
8 Nov
'06
2:41 p.m.
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