User storage occupancy

A storage occupancy count measures the area under the curve of user-task storage in use against elapsed time. The unit of measure is the byte-unit, where the unit is equal to 1024 microseconds, or 1.024 milliseconds. For example, a user task occupying 256 bytes for 125 milliseconds is measured as follows (where ms is milliseconds):
125 / 1.024 ms = 122 units * 256
               = 31232 byte-units
Note: All references to Start time and Stop time in the calculations below refer to the middle 4 bytes of each 8 byte Start/Stop time field. The Start and Stop time fields are standard S/390® STCK time values where bit 51 of the Start time or Stop time represents a unit of 16 microseconds.
  1. To calculate the response time and convert into microsecond units:
    Response = ((Stop time - Start time) * 16)
  2. To calculate the number of 1024 microsecond units:
    Units = (Response / 1024)
    or
    Units = ((Stop time - Start time) / 64
  3. To calculate the average user-task storage used from the storage occupancy count:
    Average user-task storage used = (Storage Occupancy / Units)
  4. To calculate units per second:
    Units Per Second = (1000000 / 1024) = 976.5625
  5. To calculate the response time in seconds:
    Response = (((Stop time - Start time) * 16) / 1000000)
During the life of a user task, CICS® measures, calculates, and accumulates the storage occupancy at the following points:
Figure 1 shows a pictorial representation of how the user storage occupancy measurement is calculated.
Figure 1. Transaction user storage occupancy
  │                                                                               │
  │←────────────────────────────────Response Time────────────────────────────────→│
  │                                                                               │
 S│                                                                               │S
 T│                                                                               │T
 A│              ┌───────────────────┐                                            │O
 R│              │                   │                                  ┌─────────┤P
 T│    ┌────┐    │                   │              ┌─────────┐         │         │
  │....│....│....│...................│..............│.........│.........│.........│T
 T│    │    └────┘                   └────┐         │         │         │         │I
 I│    │    .    .                   .    │         │         │         │         │M
 M├────┘    .    .                   .    └─────────┘         └─────────┘         │E
 E│    .    .    .                   .    .         .         .         .         │
  │    .    .    .                   .    .         .         .         .         │
  │    .    .    .                   .    .         .         .         .         │
  └───────────────────────────────────────────────────────────────────────────────┘
       G    F    G                   F    F         G         F         G
 
       G = GETMAIN
       F = FREEMAIN
       Dotted line = Average storage occupancy