1 Aug
2013
1 Aug
'13
12:18 p.m.
The 64K/256K could be upgraded with trivial ease to 640K, by replacing two
rows of 64K chips with 256K chips, and adding one additional chip (don't
remember what that add-on chip was.
As could the 5160 motherboard. The extra chip is a 74S158 or 74F158, it
goes in the spare 16 pin socket in the middle of the logic (if you see
what I mean). You also had to add a jumper (on the EX it's solder a link
from E1 to E2).
My XT Techref includes schematics for a '256K-640K system board'. The
only difference between that and the 64K0-256K one is that the extra
mulitplexer chip is shown and pands E1 and E2 are shown with a link
between them.
When the XT was released the PC was upgraded to 4
rows of 64K DAM for 256K
max. I bought my IBM 5150 in March 1983. (Just before the XT came out.)
XT
eliminated the cassette port, and incresed from 5 to 8 slots, although
ONE slot (closest to the power supply) skipped one buffer and was
incompatible with some cards. IBM solved THAT by plugging the hole with a
"FREE!!!" serial/20mA card (which they had excess inventory of, and
couldn't sell well because EVERY multi-funcion card had serial.