From: vulture@imperial.ac.uk (Thomas Sippel - Dau)
Newsgroups: comp.sys.sgi
Subject: Re: Indigo R4k/IBM 6k comparison
Date: 11 Jan 93 12:44:42 GMT
Reply-To: cmaae47@imperial.ac.uk
Organization: Imperial College of Science, Technology and Medicine

In article <8378@news.duke.edu>, rla@canctr.mc.duke.edu writes:
- Greetings.  We are considering a purchase of a set of 4 workstations to be
- linked together.  Objectives are mainly processing (number-crunching) power
- plus the ability to run the GCG DNA sequence analysis suite of programs.
- The two remaining candidates are SGI (R4000-based) vs. IBM RS6000s.
- 
- Anyone with experience on both platforms, including service and reliability
- and UNIX performance, please let me know your thoughts.  Overall system
- speed is a major consideration.  The IBM is not yet GCG-ready, but a
- beta-version will supposedly be ready soon.
- Thanks.

On number crunching, the RS/6000 chip will be about five times as fast as 
the R4000 on a cycle basis. This means that for a program that has

     do 10 i = 1, n
  10 sum = sum + x1(i)*y1(i) + x2(i)*y2(i) + x3(i)*y3(i) + x4(i)*y4(i)

as the inner loop where it spends its time, the R4000 will spend about
100 cycles on that loop, while the RS/6000 will do it in about 20. You can
therefore expect a 100 MHz R4000 to need 2.5 times as much time as a 50 MHz
RS/6000. The actual numbers are data dependent, because the RS/6000 needs
a cycle more for a floating point instruction if the result after 
normalisation is 0.

Having said that, if you want to do DNA sequence analysis, than I guess you
need fast disk access and generate graphics interactively with good response
times, and unfortunately that is where the IBM machines do not shine.
If there is a number crunching job with reasonable paging in the background,
the IBMs I have used here feel decidedly heavy going, while you hardly 
notice it on an Indigo.

Regarding service and reliability, both systems come with a fair sprinkling
of bugs and features you may find undesirable, and hardware reliability 
is similar (especially that of third party disks and memory :-). It more
depends on whether the actual bugs bite you or leave you alone. The "I wanna
do it exactly as on my standard BSD 4.x system" approach is guaranteed to 
lead to tears on both.

IBM has tried to make the system safe by conservative design, while SG often 
takes a more aggressive or "risky" approach - maybe it is just that IBM 
systems take longer until the organisation ships them, the old big firm
vs small firm argument.

We have however found in several cases that when a user maintained system 
suffers an unexplained failure which causes people to react in panic and destroy
whats left of it by mistaken recovery attempts, then the IRIS will normally
be up again by the third day, the IBM by the fifth. Notabene this is from
a small number of incidents. 

Hope this helps.                        Thomas

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