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From: milne@ics.uci.edu (Alastair Milne)
Newsgroups: comp.arch
Subject: Re: Complex Instructions
Message-ID: <13445@paris.ics.uci.edu>
Date: 6 May 89 07:30:34 GMT
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prem@crackle.amd.com (Prem Sobel) writes
>Many years ago, there was a machine called the Interdata Model 70 which
>had instructions for atomically adding or removing items from circular
>double ended queues. The data structure was defined reasonable effeciently
>and the machine was microcoded.
>
>Yet no one, no compiler seriously used these instructions. The reason was,
>amazingly, that individual instructions were faster!!! I never looked at
>the microcode, so I cannot commebnt why that was.

    Is this sort of finding not precisely the reason behind RISC architecture?
    The realisation that many an instruction to handle a relatively
    sophisticated job turned out to be slower than a series of very simple
    instructions to do the equivalent thing?

    I myself am not quite clear yet on why this should be ( is there perhaps a
    reason that larger, more sophisticated microcode routines can't be made
    optimally fast?).  Yet it does seem to be a fact of life.  


    Alastair Milne