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From: John Levine <johnl@taugh.com>
Newsgroups: comp.arch
Subject: Re: architecture, The Design of Design
Date: Thu, 9 May 2024 02:10:17 -0000 (UTC)
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According to Tim Rentsch  <tr.17687@z991.linuxsc.com>:
>> 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).

They were pretty close but it says on the intertubes that the -30 put
memory words 9 apart on the drum and the -21 put them 18 apart, which
I presume means that you would need to arrange your data differently
to get good performance.

>Another example may be the IBM 709 and IBM 7090, both done in the 1950s.

They were pretty similar but the 7090 had a more complex channel and
new instructions to manage it. There was a trap mode that caught the
old I/O instructions they used to run 704 or 709 coe on a 7090 but of
course not vice versa.

Compare that to S/360 where every model had the same channel
interface, the same I/O instructions, and the same I/O interrupts.

-- 
Regards,
John Levine, johnl@taugh.com, Primary Perpetrator of "The Internet for Dummies",
Please consider the environment before reading this e-mail. https://jl.ly