Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!cs.utexas.edu!yale!spock!eric
From: eric@spock.UUCP (Eric Volpe)
Newsgroups: comp.sys.dec
Subject: Re: Can a DECstation replace a 11/750 ?
Message-ID: <1990May4.025422.8656@spock.UUCP>
Date: 4 May 90 02:54:22 GMT
References: <36119@prls.UUCP> <5070@hub.ucsb.edu>
Reply-To: eric@spock.UUCP (Eric Volpe)
Distribution: usa
Organization: Choate Rosemary Hall, Wallingford CT
Lines: 37

In article <5070@hub.ucsb.edu> aks@somewhere.ucsb.edu (Alan Stebbens) writes:
>
>Again.  It appears that you are overly concerned with size, and not
>performance.  The DS3100 really runs at 15 MIPS, which is *fifteen*
>times faster than a VAX/780.  If a VAX/780 could support 8 users, why
>can't a machine which runs faster?  Again, size has absolutely nothing
>to do with performance.

It is *not* *fifteen* times faster than a vax 780! the DS3100 is a RISC
machine, meaning Reduced Instruction Set - Which means that each instruction
on a RISC processor is very small and the equivalent of several instructions
of a non-RISC processor. So, while it may be true that the DS3100 can
execute fifteen times as many of its instructions in one second as a VAX780
can of vax instructions, you're comparing apples and oranges. Each Vax
instruction accomplishes perhaps the equivalent of eight DS3100 instructions.

I'm not saying that the DS3100 isn't faster than a vax780 anyway, I'm just
saying that you can't blindly quote MIPS ratings and expect it to truly
reflect the relative performance of two totally different architectures. 

Also, Instructions per Second is not a complete description of the power
of any computer - there are many other considerations; for example, Bus
I/O speed, transfer rate, caching, etc. I'm not sure what kind of bus the
DS3100 has (is it Qbus? I haven't gotten mine yet) but the Vax780 has a very
fast bus indeed, and as far as handling many terminals, a fast bus is far
more important than a fast processor - my PDP-11/34 can handle 8 users
better than a fast DOS machine with an 8 terminal board, though the AT 
processor is indisputably much faster. So you have to look at many factors
to be able to judge the relative power of two different processors. 

						Eric Volpe


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Eric Volpe					  ...uunet!hsi!yale!spock!eric
Choate Rosemary Hall '90			[.sig still under construction]
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