17 Sep
2015
17 Sep
'15
9:47 a.m.
-----Original Message-----
From: cctalk [mailto:cctalk-bounces at classiccmp.org] On Behalf Of Noel
Chiappa
Sent: 17 September 2015 13:39
To: cctalk at classiccmp.org
Cc: jnc at mercury.lcs.mit.edu
Subject: Re: ENIAC programming Was: release dates of early microcomputer
operating systems, incl. Intel ISIS
Thanks Noel, I will have a browse of that...
From: Dave Wade
Crispin Rope concentrates on the power of ENIAC
and its usefulness
Which is why you should look at the longer, later article:
http://eniacinaction.com/wp-
content/uploads/2014/02/EngineeringTheMiracleoftheENIAC-scanned.pdf
in particular the part I pointed out (bottom right
corner of pg. 51),
which talks
about all the things that can be found in that early
ENIAC code, e.g.
subroutine calls with storage of return point, etc.
I am far less interested in the comparison with other machines (in that
article) than I am with the enumeration of what the 'program ENIAC'
_itself_
could do - which seems to have been quite a lot.
AMD29K isn't "Modern", but when used like that it's a programmable
calculator, a very sophisticated one yes......
... If you have to use another external mechanism to arbitrarily change the
program, then it's a calculator.....
.. So a PIC chip for example.....
Where It gets grey is that a Turing machine gets round this by assuming the
tape has infinite length.
I think (but am not sure) is that in effect whilst you can't have self
modifying code you have enough storage for all possible programs...
to me a "computer" without
self-modifying code is a programmable
calculator even if it has index registers...
So a modern Harvard-architecture machine (e.g. AMD29K) with only ROM on
the instruction bus is a programmable calculator?
It's precisely that hypothetical which leads me to conclude that the fact
that
the 'program ENIAC' only had ROM for its code
(actually, technically,
that's
quite not true - it could execute programs stored on
cards, too) is not
that
important; I think the thing to look at is what its
programs could contain
I think the important things end up being hypothetical, Its more WHY was it
designed so its programs COULD contain what they could contain..
Noel
Dave