This extension is enabled by default. It may be disabled by using the following option at compile time: --disable-session
To use shared memory allocation (mm) for session storage configure PHP --with-mm[=DIR].
The Windows version of PHP has built-in support for this extension. You do not need to load any additional extensions in order to use these functions.
Note:
By default, all data related to a particular session will be stored in a file in the directory specified by the session.save_path INI option. A file for each session (regardless of if any data is associated with that session) will be created. This is due to the fact that a session is opened (a file is created) but no data is even written to that file. Note that this behavior is a side-effect of the limitations of working with the file system and it is possible that a custom session handler (such as one which uses a database) does not keep track of sessions which store no data.