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From: sbf10@uts.amdahl.com (Samuel Fuller)
Newsgroups: comp.lang.misc,comp.arch
Subject: Re: Fast conversions, another urban myth?
Message-ID: <9dAz02zs58y201@amdahl.uts.amdahl.com>
Date: 20 Sep 89 20:09:40 GMT
References: <832@dms.UUCP> <688@UALTAVM.BITNET>
Reply-To: sbf10@amdahl.uts.amdahl.com (Samuel Fuller)
Organization: Amdahl Corporation, Sunnyvale CA
Lines: 39

In article <688@UALTAVM.BITNET> ECULHAM@UALTAVM.BITNET writes:
>If we throw away the hardware, and do the decimal arithmetic in software,
>we get a lot simpler machine to build. But, what do the performance
>numbers look like?
> 
>Hardware ==>   .9 + 1(.1) = 1
>Software ==>   .9 + 7(.1) = 1.6
> 
>I've clearly exaggerated the performance gain of the decimal hardware.
>Yet even with that, all that extra hardware cannot even double the
>performance of the system.
> 
>Clearly, decimal arithmetic is one of those high cost, low payback
>extensions. We should direct our efforts elsewhere.

If a few extra chips can give a machine 60% better performance
on the workloads that customers run, then it makes no sense to
not put the chips in.
A little extra complexity in the CPU will not increase the overall
system cost by 60%.  However, the 60% increase in performance over
competitors (who went the software route), will allow a 60% premium
in the price of my machines, and its all gravy.

If you are building scientific workstations then decimal hardware will
be just wasted gates.

If you are building business machines, where COBOL is still the language
of choice, then to not do decimal arithemetic in hardware is taking a
very big chance.
-- 
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Sam Fuller / Amdahl System Performance Architecture

I speak for myself, from the brown hills of San Jose.

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