24 Apr
2008
24 Apr
'08
11:45 a.m.
Eric Smith wrote:
Jules wrote:
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
didn't exist!)
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). 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
boards...
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?
cheers,
Jules