Multiprocessing and multiprogramming observations (summary)

A few observations on tightly coupled multiprocessing, loosely coupled multiprocessing, and multiprogramming within the z/TPF system architecture, are instructive:

• In a loosely coupled complex in which all CPCs are uniprocessors, there is no need for the tightly coupled multiprocessing system programming constructs. In this case, each CPC is a single I-stream engine with a private main storage where separate copies of programs are processed.
• In an environment of a single CPC that consists of a z/Architecture® configuration of multiple I-stream engines, there is no need for an XLF, because all module data is directed to a single CPC where it is managed in the z/TPF system by a single I-stream engine.
• Loosely coupled is more accurately described as the synchronization of multiple CPCs sharing a set of modules, where each CPC can be composed of multiple I-stream engines. From the viewpoint of module synchronization, each CPC is a single I-stream engine.
• A communication mechanism, called interprocessor communications (IPC), coordinates activity among CPCs in a single loosely coupled complex by using the multi-processor interconnect facility (MPIF).
• A z/TPF system can be configured without loosely coupled multiprocessing. However, tightly coupled multiprocessing constructs are always in place.
• The basic component of performance in the z/TPF system, multiprogramming, is basic to the design of the z/TPF system. This makes it possible for several Entries to be in progress at any one time, thereby enhancing performance.
• Associating workload to I-streams through the flexible use of I-stream affinity and managing or scheduling that workload is an integral part of the z/TPF system operational structure, which further enhances multiprogramming.