Using a service request block (SRB)

There are many advantages to the use of multiple virtual address spaces. Virtual addressing permits an addressing range that is greater than the central storage capabilities of the system. The use of multiple virtual address spaces provides this virtual addressing capability to each job in the system by assigning each job its own separate virtual address space. The potentially large number of address spaces provides the system with a large virtual addressing capacity.

With multiple virtual address spaces, errors are confined to one address space, except for errors in commonly addressable storage, thus improving system reliability and making error recovery easier. Programs in separate address spaces are protected from each other. Isolating data in its own address space also protects the data.

In a multiple virtual address space environment, sometimes applications need ways to communicate between address spaces. There are two basic methods of inter-address space communication:

Scheduling a service request block (SRB), an asynchronous process described in this information.
Using cross-memory services and access registers, synchronous processes that are described in z/OS MVS Programming: Extended Addressability Guide.