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From: John Levine <johnl@taugh.com>
Newsgroups: comp.arch
Subject: Re: IBM architectural goals, Byte Addressability And Beyond
Date: Thu, 30 May 2024 15:37:52 -0000 (UTC)
Organization: Taughannock Networks
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According to Michael S  <already5chosen@yahoo.com>:
>> They never remove anything from the architecture. If you're asking
>> about decimal FP, it's still there, both scalar and vector.
>
>I was talking/asking about CU14. I never had doubts about decimal
>stuff.
>You did mentioned that CU14 is a public instruction in your other
>post. It means that it can't be removed even if later proven useless.

They added two instructions to convert between UTF-8 and UTF-16 in S/390, then 
the other six among utf-8/16/32 in the initial zseries.

The only thing IBM has ever removed from the instruction set visible
to applications was the ASCII mode bit from S/360 to S/370, keeping in
mind that what they called ASCII was not what anyone else called
ASCII. Everything else is still there. 

The cost of trying to track down and patch all of the customer dusty
decks that might use obscure instructions is high, while the cost of
leaving them in the instruction set is low since it's all vertical
microcode anyway.

I've seen a presentation that said the original implementation of
decimal FP was all in millicode, while later models added hardware.
Evidently the wall street types really like the consistent decimal
rounding.



-- 
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