Persistent or working memory segments in Virtual Memory Manager

AIX® distinguishes between different types of memory segments. To understand the VMM, it is important to understand the difference between working and persistent segments.

A persistent segment has a permanent storage location on disk. Files containing data or executable programs are mapped to persistent segments. When a JFS or JFS2 file is opened and accessed, the file data is copied into RAM. VMM parameters control when physical memory frames allocated to persistent pages should be overwritten and used to store other data.

Working segments are transitory and exist only during their use by a process. Working segments have no permanent disk storage location. Process stack and data regions are mapped to working segments and shared library text segments. Pages of working segments must also occupy disk storage locations when they cannot be kept in real memory. The disk paging space is used for this purpose. When a program exits, all of its working pages are placed back on the free list immediately.