IBM 5100

From: emx <>
Date: Sun Aug 8 21:35:57 2004

Here is a post that was made on one of the web sites dedicated to John


Just a quick note on the 5100.

I'm not sure if anyone else has posted anything about the 5100, but
this machine was very interesting. In the early 80's, I worked on a
slightly upgraded version of the 5100 called the 5110. The 5100/5110
machine executed code intended for IBM mainframes of the time (System
360/370) via a simple processor that emulated the old 360/370 CPU.
Languages, such as APL or VS BASIC were programs written in machine
language, that were, in turn, interpreted by the CPU in a lower level
language called 'Microcode'

Microcode allowed IBM to modify or enhance basic machine language
instructions at will after the mainframe was delivered to the
customer. The concept was 'ship an initial version of the 'machine',
but allow upgrades as they were developed without the wholesale
replacement of hardware'. To change a basic instruction in
microprocessors today usually requires a physical change in the chip,
since all instructions are 'hard-wired' into the design of chip.

The core design of the 5100 series machine was an emulator of the old
IBM 360/370. The CPU of these machines was designed to execute the
exact same microcode of the giant mainframes which preceded them. In
fact, the 5100 shipped with a ROS (Read Only Storage, rather than ROM,
Read Only Memory) card that contained the microcode for the 370
mainframe computer CPU. Any program designed for the 370 could,
theoretically, run on the 5100 or 5110.

IBM shipped either VS BASIC or VS APL, written in IBM machine language
for the 370, on a ROS card in each 5100. No need to recompile, no need
to change much, since the little 5100 ran the exact same code as the
mainframe. It was not a fast machine, but it worked, and the
performance of the old 5100 was good enough to run many of the same
applications we had developed on our $10 million twin IBM 370
mainframe installation. APL and VS BASIC apps ran with little or no
modification, except for storage device definitions, which were
limited to 300KB 8" floppies or 150KB streaming tape cartridges.

If 'John Titor' had access to the endless library of old IBM
applications written for the 370 (and later 30X0 and 970 series)
machines in his time, a 5100 would be a handy, lightweight, SMALL
device that could be transported back to his time to run this code.
Certainly, no old 370 or subsequent compatible machines from IBM would
be available in 2036 to run this code, but a 5100 could do it, and
could be moved via his 'time machine'. The basic 5100 machine weighed
about 70 pounds and looked like a suitcase.

How much software would be available? IBM salesmen used to carry
around a little 1.5" thick book of applications written for all
possible businesses, from paint manufacturers to hog farming
operations that could be installed on any generic IBM 370 compatible
mainframe. One can STILL see companies all over the Earth running code
that was written many years ago, installed on newer hardware, but
running the exact same instructions used in the late 60's, mid-70's.

If 'John Titor' and his tales of time travel are a hoax, the inclusion
of the 5100 is a remarkable bit of technology that is quite plausible
for a society that needs basic data processing, but lacks working
hardware and working applications. It's -astonishingly- plausible. I
mean no disrespect to those who believe the 'John Titor' story, but
only wish to point out the masterful inclusion of something that
really could be true. Imagine a 2030's recon group accessing an old
IBM branch office, with old archives of business applications stored
on old tapes, just waiting for the correct hardware to run on. It
would be a virtual gold-mine, with the right hardware...

Saturday, August 7, 2004, 1:42:33 PM, you wrote:
> Hello ClassicCmp friends,
> Right now as I type this an interview is in progress on the
> Coast to Coast AM late night radio talk show about a supposed
> time traveler who went back from 2036 to 1975 to obtain a
> classic computer, specifically IBM 5100.  Needless to say,
> this story got me highly intrigued.
> Since I don't really know anything about the machine in question,
> I thought I would ask the collective list wisdom.  There must have
> been something really special about IBM 5100 for them to go back
> for it from 2036.  Does anyone know anything about that machine?
> MS
Received on Sun Aug 08 2004 - 21:35:57 BST

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