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  • Re: millicode, extracode, fractional PCs

    From John Levine@21:1/5 to All on Fri May 2 17:26:19 2025
    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

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  • From moi@21:1/5 to John Levine on Fri May 2 20:00:26 2025
    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.

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