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From: anton@mips.complang.tuwien.ac.at (Anton Ertl)
Newsgroups: comp.arch
Subject: Re: backward architecture, The Design of Design
Date: Thu, 09 May 2024 12:13:47 GMT
Organization: Institut fuer Computersprachen, Technische Universitaet Wien
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Michael S <already5chosen@yahoo.com> writes:
>On Thu, 9 May 2024 08:19:39 -0000 (UTC)
>> The term comes from Brooks.  Specifically, he applied it to the
>> S/360 line of computers which had a very wide performance and
>> price range, and programs (including operating systems) were
>> binary compatible from the lowest to the highest performance and
>> price machine.
>
>
>I suppose, it means that my old home PC (Core-i5 3550) is downward
>compatible with my old work PC (Core-i7 3770). And my old work PC is
>upward compatible with my old home PC.

Given that both use Ivy Bridge CPUs, there is no compatibility issue
as far as the CPU is concerned.  For other parts of the PCs, one would
have to discuss everything separately.

When it comes to upwards/downwards, you would have to compare with
Saltwell or Silvermont.  Ivy Bridge supports AVX, while Saltwell and
Silvermont don't.

AMD is somewhat better at these things: They added AVX support to
their small cores in 2013 (Jaguar) and their big cores in 2011
(Bulldozer), while Intel added AVX to their small cores in 2021
(Gracemont) and to their big cores in 2011 (Sandy Bridge).

For AVX2, AMD added it to their big cores in 2015 (Excavator), but by
that time they had given up on the two-pronged approach and were on
the way to the one-size-fits-all Zen line.

>But I still don't know if it would be correct to say that my old work
>PC is downward compatible with with my just a little newer small FOGA
>development server (E3 1271 v3).

Haswell is a successor to Ivy Bridge and supports AVX2 (unlike Ivy
Bridge).  So it's an unidirectional compatibility.

- anton
-- 
'Anyone trying for "industrial quality" ISA should avoid undefined behavior.'
  Mitch Alsup, <c17fcd89-f024-40e7-a594-88a85ac10d20o@googlegroups.com>