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From: Tim Rentsch <tr.17687@z991.linuxsc.com>
Newsgroups: comp.arch
Subject: Re: architecture, The Design of Design
Date: Wed, 08 May 2024 02:27:02 -0700
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Michael S <already5chosen@yahoo.com> writes:

> On Mon, 06 May 2024 18:22:59 -0700
> Tim Rentsch <tr.17687@z991.linuxsc.com> wrote:
>
>> I don't buy it.  An architecture is just a description of system
>> behavior, and surely there were descriptions of system behavior
>> before System/360.  Even in the 1950s companies must have changed
>> implementations of a given model while still conforming to its
>> earlier description.
>
> Were they?
> My impression is that until S/360 there was no such thing as different
> by 100% SW compatible models.

I think a counterexample is the LGP-30 (1956) and its successor
the LGP-21 (1963).  (For reference System/360 and OS/360 were
announced in April 1964.)  I expect there are other examples
but it's hard to get the historical data needed to answer the
question.  Another example may be the IBM 709 and IBM 7090, both
done in the 1950s.