Address space
An isolated pocket of memory in which a program runs, so that one program cannot interfere with another.
Also written region
An address space is z/OS's unit of isolation. Each one is a separate region of memory with its own view of the machine, and a program running in one cannot reach into another. It is roughly what other operating systems call a process, though address spaces tend to be longer-lived and larger in scope.
Everything running on the system occupies one. Your interactive session gets an address space when you log on. Each batch job runs in its own. Subsystems such as CICS and DB2 run in theirs, often several apiece.
The isolation is what allows a mainframe to run thousands of pieces of unrelated work at once without them corrupting each other, and it is why a badly behaved program generally takes down only itself.
You will meet the term when looking at what is running on a system, and when reading messages that identify which address space produced them. Knowing it simply means "the thing a running program lives in" is enough to get started.
Related terms
- z/OSThe main operating system that runs on IBM mainframes, in the same way Windows or Linux runs on a laptop or server.
- Started taskA long-running program that the system starts and leaves running, rather than a job that runs once and finishes.
- JobA unit of batch work submitted to the system, made up of one or more steps that run in order.
- LPARA logical partition: one physical mainframe carved into several independent virtual machines, each running its own operating system.