IBM 5120

From: <(>
Date: Thu Sep 18 14:05:56 1997

>>>My second job as a computer programmer put me in front of an IBM 5120.
>>>It was a desktop model which incorporated a B&W monitor, keyboard, and
>>>two 8" floppy drives in the main cabinet.
> Sounds like an early Datamaster to me. I have a Datamaster (5123), but it has
> a green-screen, not a B&W one. Otherwise the description matches.

Interesting. My datamaster is a 5322, and calls itself System/23. It
doesn't match the 5120 description except in the eight-inch drives. In
particular it does not blank the screen (that I recall) during I/O. The
screen is green; the keyboard is built into the system unit but looks
very like an early PC keyboard.

A brief speculation on IBM numbering. 5123 is probably a derivative of
5120 in some sense. 5322, on the other hand, looks like a variety of
System/32 (the 5320). System/32 begat System/34 (5340) begat System/36
(5360 = large, 5362 = desk side, 5364 = dekstop) begat AS/400 (I think).
System/38 also fits in there somewhere (5380) so you would expect a
System/23 to be called 5230.

> As I understand the Datamaster, it really was the predecessor to the PC. It
> was desktop based, although you needed a large desk <g>. It had an ISA-like

Nonsense! I've got mine on a very small desk! However, system unit and
printer between them take up the whole desk.

> bus into which you could plug-in cards. My guess, from talking to someone who
> worked on the project, that it was a business machine (A/P, billing, word
> processing, etc.) that fell out of favor when IBM introduced the PC in 1981.

It was indeed. There were two video options, Data Processing and Word
Processing. The DP video card had one byte per screen character, the WP card
having two. The difference to the user was that on the WP you could set the
attributes (blink, underline, intensify, inverse video) for each character
individually; on the DP model you used up a character space to make the change,
which then took effect until another attribute code appeared further down the

Mine, being a DP model, came with some sort of accounting application that I've
never used.

CPU was an 8085, using bank switching to access 128k each of RAM and ROM. Very
slow. The large ROM, though, had almost a complete mainframe basic with matrix
operations and all sorts.

Character code was EBCDIC, unlike the PC. What did 5100 use?

> The PC was 1/3 the size, probably 1/4 the weight, much faster, and used 5-1/4"
> diskettes.

And less than 1/4 the price. The previous owner of my datamaster paid
L11000 for it in 1980. The PC when it came out in the UK (1983?) was
L2399 I think.

> There are several Datamaster owners here who can fill in more about the
> actual specs. I don't use mine much because I have a blown ROM chip that
> prevents me from booting...

I was hoping that one of those hand-held machine EPROMS advertised here
a few weeks ago might act as a replacement. (No, I haven't forgotten!)

Received on Thu Sep 18 1997 - 14:05:56 BST

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