Aucbvax.2693
fa.works
utzoo!decvax!ucbvax!works
Fri Aug 14 15:30:45 1981
WorkS Digest V1 #6
>From DUFFEY@MIT-AI Fri Aug 14 15:25:28 1981
WorkS Digest Fri, 14 Aug 1981 Volume 4 : Issue 6
Today's Topics:
Workstations - IBM's Personal Computer, Micro Benchmarks
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Date: 13 Aug 1981 1159-EDT
From: Willie Lim <WLIM MIT-XX AT>
Subject: IBM Personal Computer
IBM announced its new 8080 based personal computer yesterday.
The prices range from $1500 to $6000 (approx.). It seems
that the system has color graphics. Does anyone has any
more details on the system? What is the OS on the system
and what are options?
Willie
------------------------------
Date: 13 Aug 1981 0813-PDT
From: Stevan Milunovic <MILUNOVIC SRI-KL AT>
Subject: Micro Benchmark Units
The units in the benchmark chart sent Aug 12 were bytes for
code, and microseconds for execution time. Sorry for the
omission. -Steve
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Date: 14 Aug 1981 0448-PDT
From: SCHIFFMAN at SRI-KL
Subject: Benchmarking new Micros
I forget where I first heard it said that benchmarking was Advanced
Lying With Statistics....
I looked rather carefully at the EDN benchmarks when they first
came out. I took these more seriously than usual because:
They were in Assembly language; therefore they measure
programmer skill plus machine performance, as opposed to
higher-level-language benchmarks which measure programmer
skill plus machine performance plus compiler quality.
(Worse yet are benchmarks written in different languages
for different machines which throw "language- quality"
into the mix... or benchmarks running on time-sharing
systems that end up measuring scheduler fairness and
disk performance.)
They were written by employees of the respective manu-
facturers who were likely to be skilled with the given
architecture. This also removes the possibility of
unfair advantage given due to hidden prejudices.
A reasonable coverage of routine types were made that
collectively might represent "general performance".
(Including interrupt service routines was a good move,
for example.)
Nevertheless, the benchmarks were about as useless as benchmarks
usually are!
To pick some specific nits--
Although there was ONE environmental parameter supplied (the
clock speed for the given processor) there was no mention of
what memory performance is required to run at that speed
without wait states. I believe it is the case that a 10Mhz
8086 can run with memory much slower (and therefore cheaper)
than a 10MHz 68000. Nor is it mentioned what the availability
of the part is at that clock rate. Did you know that a 10MHz
8086 is $200 cheaper than a 10Mhz 68000? Maybe if you paid
that kind of money to Intel they would sell you a 16MHz part!
The benchmark specifications had loopholes in them which
were taken (quite understandably) to differing advantage.
For example (as best as I can remember) the interrupt
service benchmark did not specify that context had to be
completely saved. The Intel programmers went ahead and
saved all registers anyway (a reasonable thing for a
service routine to do). The programmers for the other
machines only saved the minimal context necessary to meet
the specification.
So much for GOOD benchmarks!
Any yet one often hears that "CPU X is 20% faster than CPU Y"
based on even less careful comparisons.
{BTW, I'm planning to use the 68000 in my next system. And
I do think that is much faster than the 8086 for the things
I want to do. But it's very likely a bit slower (for what
I want) than the Z8000. Don't forget that there are other
reasons for choosing a CPU than how fast it goes.}
Most CPU designers, when pressed, will agree that there is no
reasonable way to collect a small set of general metrics that
will characterize machine performance. To find the fastest
among several computers "in the same performance class" can
only be done by carefully attempting to model the application
for which the machine is to be used. If you are lucky, this
can be as simple as designing your program and coding the
inner loops for each machine to be considered. If you're not
so lucky, you might spend a year building a workload simulator
and still not know how different things will be if you get a
different disk controller.
Doing it right, of course, can be very hard. It's much easier
to refer to a list of how long a quicksort of 100 items takes
for every machine ever invented.
Joseph Weisenbaum (in "Computer Power and Human Reason") tells of
the story about the drunk repeatedly walking around a lamp post
at night. A passing policeman asks him for an explanation. The
drunk replies that he lost his keys--
Cop: "Oh, so you lost them under the lamp post?"
Drunk: "Naw, lost 'em over there." (Waving at the distant
darkness).
Cop: "So why look for them under the lamp?"
Drunk: "Silly! 'Cause the light's so much better here!"
-Allan
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End of WorkS Digest
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