[inforoots] bits again

[Hans Neukom]

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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