Editing Virtual memory (section)

==Address space swapping==
Some operating systems provide for swapping entire [[address space]]s, in addition to whatever facilities they have for paging and segmentation. When this occurs, the OS writes those pages and segments currently in real memory to swap files. In a swap-in, the OS reads back the data from the swap files but does not automatically read back pages that had been paged out at the time of the swap out operation.

IBM's [[MVS]], from [[OS/360 and successors#OS/VS2 SVS and MVS|OS/VS2 Release 2]] through [[z/OS]], provides for marking an address space as unswappable; doing so does not pin any pages in the address space. This can be done for the duration of a job by entering the name of an eligible<ref>The most important requirement is that the program be APF authorized.</ref> main program in the Program Properties Table with an unswappable flag. In addition, privileged code can temporarily make an address space unswappable using a SYSEVENT [[Supervisor Call instruction]] (SVC); certain changes<ref>e.g., requesting use of preferred memory</ref> in the address space properties require that the OS swap it out and then swap it back in, using SYSEVENT TRANSWAP.<ref>{{cite web |title=Control swapping (DONTSWAP, OKSWAP, TRANSWAP) |series=z/OS MVS Programming: Authorized Assembler Services Reference SET-WTO SA23-1375-00 |url=http://pic.dhe.ibm.com/infocenter/zos/v2r1/index.jsp?topic=%2Fcom.ibm.zos.v2r1.ieaa400%2Fswap.htm |date=1990–2014 |website=IBM Knowledge Center |access-date=9 October 2016}}</ref>

Swapping does not necessarily require memory management hardware, if, for example, multiple jobs are swapped in and out of the same area of storage.