Article View: comp.arch
Article #21078Re: Complex Instructions
From: Alastair Milne
Date: Sat, 06 May 1989 07:30
Date: Sat, 06 May 1989 07:30
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1605 bytes
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
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Path: arc1-ca.pugleaf.net!utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!husc6!bbn!usc!orion.cf.uci.edu!uci-ics!ics.uci.edu!milne 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 References: <57252@yale-celray.yale.UUCP> <4101@tolerant.UUCP> <134@dg.dg.com> <39609@think.UUCP> <25384@amdcad.AMD.COM> Sender: news@paris.ics.uci.edu Reply-To: Alastair Milne <milne@ics.uci.edu> Distribution: na Organization: Educational Technology Center, Dept. of ICS, UC Irvine Lines: 21