Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!purdue!gatech!prism!loligo!mccalpin
From: mccalpin@loligo.cc.fsu.edu (John McCalpin)
Newsgroups: comp.arch
Subject: Re: Bandwidth and RISC vs. CISC
Message-ID: <632@loligo.cc.fsu.edu>
Date: 28 Apr 89 11:51:01 GMT
References: <1262@l.cc.purdue.edu>
Reply-To: mccalpin@loligo.cc.fsu.edu (John McCalpin)
Organization: Supercomputer Computations Research Institute
Lines: 25

In article <1262@l.cc.purdue.edu> cik@l.cc.purdue.edu (Herman Rubin) writes:

>Another example is floating point arithmetic.  The RISCy CRAY, on problems
>with rigid vectors, will run rings around the CYBER 205 in single precision
>floating point (around 14 digits).  If we now change to double precision,
>we not get a time factor of about 15 in favor of the CYBER.  Many problems
>in which non-rigid vectors are appropriate also favor the CYBER.

>Herman Rubin, Dept. of Statistics,hrubin@l.cc.purdue.edu

(1) What is a "rigid vector"?

(2) On 64-bit vector operations with long vectors, the Crays do not
    "run rings around" the Cyber 205.  The asymptotic speeds (MFLOPS) are:
		Cray-1		Cyber 205	Cray X/MP
		 160		   200		   235

(3) Both the X/MP and 205 perform "double precision" (128-bit) arithmetic
    in software, and experience a slow-down of close to a factor of 100
    relative to 64-bit vector operations.
-- 
----------------------   John D. McCalpin   ------------------------
Dept of Oceanography & Supercomputer Computations Research Institute
mccalpin@masig1.ocean.fsu.edu		mccalpin@nu.cs.fsu.edu
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