Re: millicode, extracode, fractional PCs

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.