[inforoots] bits again

[Ed Thelen]

A more appropriate question might be:

   What machine was the first to *not* require self modifying code?
   that is, a more convenient way to index?  - say using a "B-Box" ;-))
                  and set up a subroutine return? - say a stack

Ed Thelen

----- Original Message -----
From: "Hans Neukom" <hans.neukom at hispeed.ch>
To: "Open Discussion about the history of the Information Age" <inforoots at computerhistory.org>
Sent: Tuesday, November 28, 2006 1:27 AM
Subject: RE: [inforoots] bits again


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> Regarding Niels Ole Finnemann's question on Self Modifying Code:
>
> "If I may add a question I would ask: who then was first referring to or to
> practise Self Modifying code - and on which machine?"
>
> This will depend on how you define "self modifying". If you include under
> such a definition the capability to change the sequence of a stored program
> depending on intermediate calculation results, the ENIAC would be a
> contender in its later life after it had been modified to run a stored
> program using what was called the "ENIAC Converter Code" in early 1948. This
> converter code (instruction set) included conditional jump instructions and
> the means to branch to a subroutine and back.
> W. Barkley Fritz, who was instrumental in implementing the ENIAC Converter
> Code, uses the words "program modification" in this context in his article
> 'ENIAC - A Problem Solver' in the IEEE Annals of the History of Computing,
> Vol. 16. No. 1, 1994.
>
> If, however, you understand under "self modifying" the capability to change
> the op code of a stored instruction by the program itself, then ENIAC is no
> contender because the program store was read only and there was no
> "instruction register" the contents of which could be changed by the
> program.
>
>
> Hans Neukom
> Schulhausstrasse 74
> CH8704 Herrliberg
> Switzerland
> E-Mail: hans.neukom at hispeed.ch
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