24 Apr
2008
24 Apr
'08
3:07 p.m.
Chuck Guzis wrote:
Why they didn't do a lot of things when it came to the PC's design is beyond
me (even down to the choice of CPU - wasn't the m68k generally available by
the 1981 launch of the 5150?)
Some of the choices seem to have been typical revenue maximisation, but there
appears to have been some real boneheaded design decisions in there too (even
in a "the PC was supposed to just be an intelligent terminal" context, let
alone as a standalone desktop machine)
Date: Thu, 24 Apr 2008 13:45:10 -0500
From: Jules Richardson
Definitely - I assume IBM's thinking was the memory expansion boards were the
way forward (rather than thinking '64KB is plenty' - which would have plainly
been stupid). And why put more memory on the system board when you could sell
customers memory expansion boards as an option? :-)
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!)
Yup, but vendors like Quadram and Everex came along pretty quickly.
Lots of folks realized that the 64K limitation was a huge one. 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...
There were also some hacks, since 64K DRAMs were available when the
5150 was launched (why IBM didn't design the planar with jumpers to
select memory type is beyond me). If you were handy with a soldering
iron and an Xacto knife, you could cut-and-jumper your way to 256K
planar memory. The big pain was the soldered-in first row of 16K
DRAM.
Y'know, I did have a document describing such a trick - I just had a look and
have absolutely no idea where I've filed it, though :(
I was happy to retire my 5150 and get a genuine
Taiwanese clone mobo
with 256K and 8 slots.
Yeah, I acquired a clone from Comcen somewhere along the line, and that was
more reasonable in terms of abilities - but in terms of vintage computer
enthusiasm (rather than serious development machine) I'd still like to get
hold of another genuine 5160 I think.
cheers
Jules