Editing Memory paging (section)

==Sharing==
In [[multi-programming]] or in a [[multi-user]] environment, many users may execute the same program, written so that its code and data are in separate pages. To minimize RAM use, all users share a single copy of the program. Each process's [[page table]] is set up so that the pages that address code point to the single shared copy, while the pages that address data point to different physical pages for each process.

Different programs might also use the same libraries. To save space, only one copy of the shared library is loaded into physical memory. Programs which use the same library have virtual addresses that map to the same pages (which contain the library's code and data). When programs want to modify the library's code, they use [[copy-on-write]], so memory is only allocated when needed.

Shared memory is an efficient means of communication between programs. Programs can share pages in memory, and then write and read to exchange data.