IBM 5150 maximum memory?
ard at p850ug1.demon.co.uk
Thu Apr 24 15:22:44 CDT 2008
> 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.
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