The Virtual Memory Manager (VMM) provides the virtual memory facilities that are used by the other parts of the system to implement the following:
The VMM implements virtual memory, allowing the creation of segments larger than the physical memory available in the system. The segments are divided into fixed-size units called pages. Each page in a segment can be in physical memory or stored on disk until it is needed. When a process accesses a page that is not present in physical memory, the VMM reads the page into memory; this is called a PageIn. When physical memory is not available, the VMM writes pages to disk; this is called a PageOut or PageSteal.
The following are some of the
|Working storage||Segments are used to implement the data areas of processes and shared memory segments. The pages for working storage segments are stored in the paging spaces configured in the system.|
|Persistent storage||Segments are used to manipulate files and directories. When a persistent storage segment is accessed, the pages are read and written from its file system.|
|Client storage||Segments are used to implement some virtual file systems like Network File System (NFS) and the CD-ROM file system. The storage for client segment pages can be in a local or remote computer.|