24 Apr
2008
24 Apr
'08
1:22 p.m.
Does anyone recall what the maximum memory was for an original IBM 5150 PC at
launch time?
The way I recall it, IBM only offered 64KB expansion cards back in the day
(256KB ones came later) and the 5150 would only take four of them (wasn't the
fifth expansion slot wired differently or something)?
No, all 5 slots on a 5150 are identical. It's the 5160 (XT) which has one
slot wired differently...
But you'd better put a display adapter (video card) in the machine, which
uses up one of the slots. I guess a floppy controller would be _useful_,
but not essential, the 5150 does, after all, have the cassette port.
That still gives a maximum of 320KB of memory though (4 x 64KB, plus 64Kb on
the motherboard) - yet I was remembering the maximum total memory as being 256KB.
Maybe that's for a disk system. 64K on the motherboard and 3 64K cards.
The other 2 slots being the floppy controller and display.
Maybe just bit-rot on my part. Or did the motherboard memory somehow get
disabled if memory expansion boards were in use? Or was there some kind of
No. You used the motherboard memory too.
maximum limit dictated by the 5150's BIOS?
I see to recall that early versions of the 5150 BIOS wouldn't take RAM
all the way to 640K. But it would go further than 256K.
-tony