APC & E-Accelerator et al, are great tools to increase performance practically instantly through Op-Code caching. Nowadays OpCode caching is actually built into PHP. But these systems have another common utility that is less frequently used which is the ability to store user variables. These variables are stored in a reserved segment of memory allocated by the extension when the Webserver starts up. Access to these variables is extremely fast since there is no disk or network overhead. Unlike a database, filesystem or network-based store like Memcache, variables created by APC et al in the Webserver SAPI are unavailable to the CLI SAPI.