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CLARIFICATION

There seems to have been a great deal of confusion over what this

benchmark measures, and how to use these results.  Let me try to clarify

this:

        1) DHRYSTONE is a measure of processor+compiler efficiency in

           executing a 'typical' program.  The 'typical' program was

           designed by measuring statistics on a great number of

           'real' programs.  The 'typical' program was then written

           by Reinhold P. Weicker using these statistics.  The

           program is balanced according to statement type, as well

           as data type.

        2) DHRYSTONE does not use floating point.  Typical programs don't.

        3) DHRYSTONE does not do I/O.  Typical programs do, but then

           we'd have a whole can of worms opened up.

        4) DHRYSTONE does not contain much code that can be optimized

           by vector processors.  That is why a CRAY doesn't look real

           fast, they weren't built to do this sort of computing.

        5) DHRYSTONE does not measure OS performance, as it avoids

           calling the O.S.  The O.S. is indicated in the results only

           to help in identifying the compiler technology.

        6) DHRYSTONE is not perfect, but is a hell of a lot better than

           the "sieve", or "SI".

        7) DHRYSTONE gives results in dhrystones/second.  Bigger

           numbers are better.  As a baseline, the original IBM PC

           gives around 300-400 dhrystones/second with a good compiler.

           The fastest machines today are approaching 100,000.

If somebody asked me to pick out the best machine for the money, I

wouldn't look at just the results of DHRYSTONE.  I'd probably:

        1) Run DHRYSTONE to get a feel for the compiler+processor

           speed.

        2) Run any number of benchmarks to check disk I/O bandwidth,

           using both sequential and random read/writes.

        3) Run a multitasking benchmark to check multi-user response

           time.  Typically, these benchmarks run several types of

           programs such as editors, shell scripts, sorts, compiles,

           and plot the results against the number of simulated users.

        4) If appropriate for the intended use, run something like

           WHETSTONE, to determine floating point performance.

        5) If appropriate for intended use, run some programs which do

           vector and matrix computations.

        6) Figure out what the box will:

                - cost to buy

                - cost to operate and maintain

                - be worth when it is sold

                - be worth if the manufacturer goes out of business

        7) Having done the above, I probably have a hand-full of

           machines which meet my price/performance requirements.

           Now, I find out if the applications programs I'd like

           to use will run on any of these machines.  I also find

           out how much interest people have in writing new software

           for the machine, and look carefully at the migration path

           I will have to take when I reach the (inevitable) limits

           of the machine.

To summarize, DHRYSTONES by themselves are not anything more than

a way to win free beers when arguing 'Box-A versus Box-B' religion.

They do provide insight into Box-A/Compiler-A versus Box-A/Compiler-B

comparisons.

                        Rick Richardson

                        PC Research, Inc.

                        (201) 389-8963 (9-17 EST)

                        (201) 542-3734 (7-9,17-24 EST)

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