The supported operating systems are listed in Table 7-3 on page 214 and Table 7-4 on  page 216. An operating system that uses SMT controls each core and is responsible for maximizing  their throughput and meeting workload goals with the smallest number of cores. In z/OS,  HiperDispatch cache optimization should be considered when you must choose the two  threads to be dispatched in the same processor.  HiperDispatch attempts to dispatch guest virtual CPUs on the same logical processor on  which they ran. PR/SM attempts to dispatch a vertical low logical processor in the same  physical processor. If that process is not possible, it attempts to dispatch it in the same node,  or then the same CPC drawer where it was dispatched before to maximize cache reuse. From the perspective of an application, SMT is transparent and no changes are required in  the application for it to run in an SMT environment, as shown in Figure 7-1. PR/SM Hypervisor MT Aware MT Ignorant z/OS z/VM Figure 7-1 Simultaneous multithreading z/OS The following APARs must be applied to z/OS V2R1 to use SMT: The use of SMT on z/OS V2R1 requires enabling HiperDispatch, and defining the processor  view ( PROCVIEW ) control statement in the LOADxx parmlib member and the  MT_ZIIP_MODE parameter in the IEAOPTxx parmlib member. The  PROCVIEW  statement is defined for the life of IPL, and can have the following values: GLYPH<SM590000> OA43366 (BCP) GLYPH<SM590000> OA43622 (WLM) GLYPH<SM590000> OA44439 (XCF) GLYPH<SM590000> CORE : This value specifies that z/OS should configure a processor view of core, in which a  core can include one or more threads. The number of threads is limited by z14 ZR1 to two  threads. If the underlying hardware does not support SMT, a core is limited to one thread. GLYPH<SM590000> CPU : This value is the default. It specifies that z/OS should configure a traditional processor  view of CPU and not use SMT. GLYPH<SM590000> CORE,CPU_OK : This value specifies that z/OS should configure a processor view of core (as  with the  CORE  value) but the CPU parameter is accepted as an alias for applicable  commands. When  PROCVIEW CORE  or  CORE,CPU_OK  are specified in z/OS that is running in z14 ZR1,  HiperDispatch is forced to run as enabled, and you cannot disable HiperDispatch. The  PROCVIEW  statement cannot be changed dynamically; therefore, you must run an IPL after  changing it to make the new setting effective. 234  IBM 14 Model ZR1 Technical Guide