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z/OS Features

One of the general capabilities that all versions of z/OS provide is multiple virtual storage support, which is the creation of 2 GB virtual storage address spaces that use auxiliary DASD storage. The introduction of 64‑bit address support in z/OS Version 1 Release 2 increases this capability to 16 exabytes with suitable CPU’s. The virtual storage technique makes real storage appear larger than it really is to applications programs. z/OS also provides support for the largest IBM processors and a component called the time sharing option (TSO). All TSO users and batch jobs have their own individual virtual storage address spaces.

z/OS performs job entry functions through one of two available job entry subsystems: JES2 or JES3.

To optimally use the hardware resources, z/OS also provide a system resource manager (SRM) or workload manager (WLM) to dynamically control the system workload. z/OS also permit dynamic allocation and deallocation of data sets. z/OS have a VSAM master catalog which supports user‑defined VSAM user catalogs. z/OS permits virtual input and output (VIO) for temporary data sets to speed up processing.

With the advent of newer IBM processors, IBM introduced a number of important facilities that made it easier to more effectively connect multiple connected processors to operate as a single cohesive system. Parallel sysplex, or sysplex, generically refers to a group of such processors that are configured as a single, logical unit that run in parallel to process an installation’s workload. A special hardware/software facility known as the Coupling Facility provides sophisticated clock management, high-speed shared storage, and high-speed communication for the interconnected processors.

A sysplex environment provides numerous advantages. For one, it is possible to dynamically reconfigure the available system resources to allow for changes in workload. For another, it provides redundancy and backup capability in the event of one or more processor failures.

Specific Coupling Facility functions include the cross system coupling facility (XCF) and cross-system extended services (XES).

XCF provides high-speed services for allowing one system to communicate with another system. Products such as CA ACF2 and CA Top Secret use XCF to broadcast console operator commands to other systems that participate as a group of connected systems, or an XCF group.

XES provides sophisticated memory caching facilities which allow for high-speed data sharing across connected systems. Products such as CA ACF2 and CA Top Secret use XES services to provide high-speed access to shared security information.