Swapping is the process of transferring all of the pages of an address space between real storage and auxiliary storage. A swapped-in address space is active; having pages in real storage frames and pages in auxiliary storage slots. A swapped-out address space is inactive; the address space resides on auxiliary storage and cannot execute until it is swapped in.
While only a subset of the address space’s pages (known as its working set) would likely be in real storage at any time, swapping effectively moves the entire address space. It is one of several methods that z/OS uses to balance the system workload and ensure that an adequate supply of available real storage frames is maintained.
Swapping is performed by the System Resource Manager (SRM) component, in response to recommendations from the Workload Manager (WLM) component.