6. DATA SOURCES › 6.7 Memory Measurements › 6.7.4 Page Seconds and Memory Service Units

6.7.4 Page Seconds and Memory Service Units

The CA MICS variables shown in the MVS memory maps in Section
6.7.2 are measures of total virtual storage amounts used by
the various parts that make up the address space of a job
step, started task, or TSO session.

There are additional measures of storage used that show real
memory used and for how long.

PAGE SECONDS

Page seconds are the product of page frames in central
storage and TCB CPU time used by an address space.  Each time
the MVS dispatcher activates a particular address space, the
TCB time is accumulated, and when an interrupt of some sort
occurs, the TCB time is multiplied by the number of active
page frames in real memory to produce a value for page
seconds.  These page seconds are accumulated over the life of
the job step or session and are reported in the SMF type 30
record for the address space.  The CA MICS variable for page
seconds is PGMPGSEC in the BATPGM, BAT_ST, BAT_TS, and BAT_TP
files.

MEMORY SERVICE UNITS

Memory service units are similar to page seconds, but with a
twist.  In Section 6.4.5, CPU service units were discussed as
a measure of work done that was repeatable on processors of
different speeds.  Memory service units are calculated
according to the following formula:

    Memory Service Units = (pages * TCB SU * SDC)/50

where:

pages =      the real pages in memory.

TCB SU =     the TCB CPU service units consumed.

SDC =        the Service Definition Coefficient for memory as
             specified in the IPS (Installation Performance
             Specifications).

50 =         a scaling factor to bring memory service in line
             with TCB, SRB, and I/O service units.

So, where page seconds will change when an application is run
on a processor with a different MIPS rating, even though its
execution is identical, MSO (Main Storage Occupancy) service
units should not change, as long as the same SDC values are
used on the new processor.  The CA MICS variable for MSO
service units is PGMMSOSU in the BATPGM, BAT_ST, BAT_TS, and
BAT_TP files.