IBM 5150 maximum memory?
jules.richardson99 at gmail.com
Thu Apr 24 13:45:10 CDT 2008
Eric Smith wrote:
> Jules wrote:
>> Does anyone recall what the maximum memory was for an original IBM 5150 PC
>> at launch time?
> My vague recollection is somewhere around (but NOT equal to) 512KB, but
> I could be wrong. The memory expansion cards IBM sold at the time
> weren't sufficient to get there, but third party cards would (and beyond).
Indeed - in the context of the discussion I got involved in (which was
actually about memory prices, not the PC specifically), we were just
interested in what could be done with a 5150 *when it was new* - and I think
all that IBM offered then was the 64K boards (and of course third parties
> You could put five of them in, but then you had no video display and
> no floppy controller. Thus normally you didn't see more than three
> of them in one machine.
You know, I had a thought - I wonder if those 64K boards can't be jumpered
beyond the 256KB boundary? Maybe that's why I'm remembering a 256KB limit on
the original machines (and using original IBM expansion boards). Getting
around that would mean physically hacking the address lines / decoding of the
But yes, fair point about the expansion boards. I expect it was unusual to see
a 5150 without floppy drives, and I don't think the things would even boot
without a display adapter (something that's plagued server PCs ever since!)
> At least one online source claims that the switch settings did go
> to 640KB. Possibly that was only on the later revision of the
> planar and BIOS?
The problem I find is that people tend to mix up the 5150 and 5160 - so things
often get quoted in the context of the 5150 that weren't true.
> The company I worked for at the time bought a PC on the day of release
> (August 12, 1981), specifically to develop third-party peripherals and
> software. The company was one of the first to market with a "combo
> card", but was never as successful with it as AST, Quadram, etc.
I wonder how many such vendors there were? Every (IBM) PC I've ever looked in
seems to have a different multi-function board from a different vendor in :)
(and of course the documentation on how to set it up is long gone)
Odd that the 5150/5160 docs/techrefs aren't on bitsavers - anyone know if
they're archived elsewhere, or are they just something that IBM still get
really upset about?
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