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From: John Levine <johnl@taugh.com>
Newsgroups: comp.arch
Subject: Re: millicode, extracode, fractional PCs
Date: Fri, 2 May 2025 17:26:19 -0000 (UTC)
Organization: Taughannock Networks
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Originator: johnl@iecc.com (John Levine)

According to moi  <findlaybill@blueyonder.co.uk>:
>On 02/05/2025 16:18, EricP wrote:
>
>> And a paper on IBM Millicode which is kind of like Alpha PAL code
>> and may be similar to Robert's mega-ops.
>> 
>> The What and Why of System z Millicode 2012
>> https://share.confex.com/share/119/webprogram/Handout/Session11773/The%20What%20and%20Why%20of%20System%20z%20Millicode%20-%20%2311773.pdf
>
>Thanks for that reference.
>
>I struggle to see how "millicode" differs in essentials from
>the "extracode" implementation of complex orders on the
>Ferranti Orion & Atlas, or the ICT 1900 Series, of 60 years ago.

It looks very similar.  The main difference I can see from extracode
is that extracode used the same hardware instruction set as normal
programs but millicode has a few extra instructions not usable
in normal programs.

Given that that deck credited Wilkes for microcode in the 1950s I'm
suprised they didn't mention extracodes.  Surely they knew about it.

-- 
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