RISC MIPS -- Sun vs. VA

[Charles Hedrick]

In the Unix marketplace, MIPS normally means performance that many times
that of a VAX 11/780, which is essentially the same as a MicroVAX 1. This
led to talk of gold-plating a 780 and giving it to the NBS as the Offical
MIP.  MIPS are normally evaluated by trying a set of benchmarks on both a
VAX and the machine involved.  (I suspect that these days they probably do
the VAX tests on a newer VAX and then divide by DEC's MVUP rating.  MVUP
is performance related to the MicroVAX 1.)

Thus MIPS is not an actual count of instructions per second.  Of course
this only gives you a ballpark idea about a machine, since the ratio will
be different for different tasks.  In general it seems like RISC machines
tend to perform somewhat better on simple tests than in reality.  MIPS
will also be different for different operating systems, so a VAX 8800
running VMS may be faster than a Sun that has the same number of "MIPS".

Sun's official rating for the Sun 4/280 was 10 MIPS.  That was based on
some early tests, but no real user experience.  I think many people now
believe that for real tasks a more typical number is 8 MIPS, with 6 MIPS
for Fortran (both integer and floating point).  Presumably Sun is keeping
its definition of MIPS constant, so you might want to multiply figures for
their newer systems by the same .8 fudge factor.

As far as I can tell "RISC MIPS" is used mostly by IBM for the RT.  It
seems to be an actual instructions per sec count.  Since RISC instructions
do less than the VAX instructions, "RISC MIPS" are worth less than the
MIPS you normally hear quoted.  The ratio is probably between 1.5 and 2.0.

Nobody is very enthusiastic about MIPS, since nobody really believes you
can characterize a machine by one number.  Furthermore, MIPS are usually
evaluated by vendors, and no two vendors use the same tests.  Digital
Review does a lot of testing of machines in the Unix marketplace and seems
to use a consistent methodology.  However their tests are almost entirely
in Fortran.  Because VMS has a particularly good Fortran compiler, this
tends to understate the MIPS of non-DEC machines.