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From: moi <findlaybill@blueyonder.co.uk>
Newsgroups: comp.arch
Subject: Re: millicode, extracode, fractional PCs
Date: Fri, 2 May 2025 20:00:26 +0100
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On 02/05/2025 18:26, John Levine wrote:
> 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.

So has extracode on the Orion and the 1900 Series.

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

Quite so.

-- 
Bill F.