Time-shared, virtual memory systems
are very complex and changes in their performance may
be caused by many factors - by variations in the
workload as well as changes in system configuration.
The evaluation of these systems can thus best be
carried out by linking results obtained from a
planned programme of measurements, taken on the
system, to some model of it. Such a programme of
measurements is best carried out under conditions in
which all the parameters likely to affect the system's
performance are reproducible, and under the control of
the experimenter. In order that this be possible the
workload used must be simulated and presented to the
target system through some form of automatic
workload driver. A case study of such a methodology
is presented in which the system (in this case the
Edinburgh Multi-Access System) is monitored during a
controlled experiment (designed and analysed using
standard techniques in common use in many other branches
of experimental science) and the results so obtained
used to calibrate and validate a simple simulation
model of the system. This model is then used in
further investigation of the effect of certain system parameters upon the system performance. The
factors covered by this exercise include the effect
of varying: main memory size, process loading
algorithm and secondary memory characteristics