ENIAC programming Was: release dates of early microcomputer operating systems, incl. Intel ISIS

Dave G4UGM dave.g4ugm at gmail.com
Thu Sep 17 11:47:50 CDT 2015

> -----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
>     > 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
Thanks Noel, I will have a browse of that...

> 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'
> could do - which seems to have been quite a lot.
>     > 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?

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...

> It's precisely that hypothetical which leads me to conclude that the fact
> the 'program ENIAC' only had ROM for its code (actually, technically,
> quite not true - it could execute programs stored on cards, too) is not
> 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


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