Shmop is an easy to use set of functions that allows PHP to read, write, create and delete UNIX shared memory segments. These functions will not typically work on Windows, as it does not support shared memory. As of Windows 2000 though, enabling the php_shmop.dll in your php.ini will enable this functionality though.
Note: In PHP 4.0.3, these functions were prefixed by shm rather than shmop.
To use shmop you will need to compile php with the --enable-shmop parameter in your configure line.
Example 1. Shared Memory Operations Overview