IBM® uses CPU service units (CPU SUs) as the measurement unit for reporting the processor's usage of a product. CPU service units, which include TCB and SRB times and represent a common unit of processor capacity across the entire S/390® line of processors, are based on standard performance benchmarks. Unlike CPU time, a CPU SU represents approximately the same processor capacity regardless of the model and type of processor. These CPU service units are described in z/OS MVS Initialization and Tuning Guide and used by system programmers to tune MVS™. They are also reported by IBM's Resource Measurement Facility™ (RMF™), except that the service definition coefficients have not been applied.