[ Previous | Next | Table of Contents | Index | Library Home |
Legal |
Search ]
System Management Concepts: Operating System and Devices
The Virtual Memory Manager (VMM)
provides the virtual memory facilities that are used by the other parts of the
system to implement the following:
- Virtual address space of
processes
- Sharing of executables
- Shared memory segments
- Mapped files.
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
segment types:
| 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.
|
[ Previous | Next | Table of Contents | Index |
Library Home |
Legal |
Search ]