All the computer's memory, usually with the exception of a small portion reserved for the operating system, is available to a single application.
A system using single contiguous allocation may still multitask by swapping the contents of memory to switch among users.
Partitioned allocation usually requires some hardware support to prevent the jobs from interfering with one another or with the operating system.
Partitions may be either static, that is defined at Initial Program Load (IPL) or boot time, or by the computer operator, or dynamic, that is, automatically created for a specific job.
MVT and successors use the term region to distinguish dynamic partitions from static ones in other systems.
Relocatable partitions are able to be compacted to provide larger chunks of contiguous physical memory.
[3] Some systems allow partitions to be swapped out to secondary storage to free additional memory.
Early versions of IBM's Time Sharing Option (TSO) swapped users in and out of time-sharing partitions.
The physical memory can be allocated on a page basis while the address space appears contiguous.
"[1]: 165 Segments are areas of memory that usually correspond to a logical grouping of information such as a code procedure or a data array.
[6] Rollout/rollin (RO/RI) is a computer operating system memory management technique where the entire non-shared code and data of a running program is swapped out to auxiliary memory (disk or drum) to free main storage for another task.