Sommaires des sites JMP La proto Informatique Le Tour du Monde de Renaud Le Yunnan  (Chine) La Birmanie Le Spiti

Computosaures > IBM650

(en français)

I have found some information concerning the IBM 650 programming.
I propose you to discover how we used this old machine.
and you will see that was not simple!
Be smart because I have difficulties to understand how that operated.
and consequently I can make mistakes...

My goal is make you discovering how these machines operated, because we can find sometimes
photographies, but we never have the possibilty to go thru the technology!
I would like young professionals understand how it was diffcult to reach 2007 technology.

Tentative description of the IBM650 programming world

IBM650 is a very old machine designed during fifties. (1954..)
It was made with vacuum tubes (or may be some transistors?) and used a magnetic drum.
Codes and datas were registered on or read from this magnetic drum.
(no magnetic cores, they were not invented)
This conducted to a particular programming technic (in decimal) which need to be care with the magnetic drum rotation.
Executive time of one instruction leaves the drum to rotate of 2 or 3 memory words.
With interlaced programming, the instruction time was only 6 words (leaving drum rotating).
Without this 'high tech' interlace, the time would be 16 times longer.
This implicated too, that instructions contained the next adress. (no ordinal pointer)

The machine did not use pure binary (octal or hexa) but a decimal coded system,
in order to be compatible with punched cards (fromm 0 to 9).
There were no ordinal pointer, so each instruction had to define the next instruction adress.

If you are interested by a better description of the 650 operation, have a look at:
IBM.650.1955.102646125.pdf i have found on
This explain operation in details. I have not completly understood..., i need to read it again!

A simulator of the IBM650 computer can be loaded at the following URL: (Be carefull, Java is needed to launch simulator)
I tried to make a simulation... but, unfortunatly, the simulator is not able to use
memories address 8003, 8002 and 8001 as memory contents of upper, lower and
Distributor registers.
(more precisely, unable to execute instruction defined in that registers)
Patches are difficult to implement and to test!

Thanks to Scott Balay, Jack Bartch, Brian Freeman, Jeremy Greene and Anne McNaughton
for their simulator.

Documents concerning IBM650

Sorry documents are in french... and programs in SOAP or decimal!


You understand that printed mater are not from me...
I don't remember the name of my professor (memory, memory)
If somebody know his name, i would be happy to write here, his name.

... The professor names are probably Georges Brillouët and Christian Coatmelec.
It's very difficult for me to certify their names because they came from Rennes University (?)
to give lectures in Nantes university, and i came from Angers University to get some
information about computing... missing lectures of my electronic cursus (Ecole d'ingénieurs)

Copyright JM Pichot, on 19 june 2007
2007-06-20 Translation
2007-07-23 modif prof names
2008-02-01 Html error correction

since 28jan2008