CPU service units are calculated by the usage report program based on the CPU time information collected in SMF type 89 subtype 1 records. The processor-dependent CPU SU factors used in this calculation are supplied by IBM® in the usage report program. The program also contains the CPU SU factors for non-IBM processors for which both IBM and the processor manufacturer have reached agreement. The CPU SU factors are commonly referred to as “SRM constants” in z/OS MVS Initialization and Tuning Guide, where they have been traditionally published for IBM processors.

Unlike the system resource management (SRM) component, which uses the logical processor configuration (LPAR when using under PR/SM™) to choose the appropriate CPU SU factor, the usage report program uses the CPU SU factor corresponding to the single image mode of the physical processor to calculate CPU service units. Consistently using the CPU SU factor for the physical processor allows installations to configure their processors in the logical configurations most appropriate to their data processing needs without incurring additional software charges due to the specifics of the logical configuration chosen.