DOCUMENT ID:  1203-02

SYNOPSIS:     Features of the SunOS Virtual Memory

OS RELEASE:   2.4

PRODUCT:      Solaris

KEYWORDS:     virtual memory process page physical vnodes


DESCRIPTION:

Features of the SunOS Virtual Memory.


SOLUTION:

*       A process's (virtual) address space is mapped onto
        objects in virtual memory.

*       Each page in virtual memory is backed by some physical
        storage, either disk or main memory.

*       A page of a process's address space can only map to
        one physical object.

*       A physical page in any given object may be mapped by
        many different process pages. Shared Libs would be 
        an example.

*       The virtual memory system operates on pages rather
        than segments in order to provide efficient copy-on-write
        facilities.

*       These physical objects are represented to the kernel by
        virtual nodes (vnodes).

Other operating systems have been segment-oriented (text, data, and
stack) rather than page-oriented.  By using a page-oriented system, a
separate copy of a page for a process is only necessary for the page
being modified.  This is only necessary if the page is mapped to private
access rather than shared. 

A vnode is a file system-independent inode.  It is used to identify an
object such as a local file, a remote file, or a device in kernel
memory. 


DATE APPROVED: 10/10/95