The phar extension provides a way to put entire PHP applications into a single file called a "phar" (PHP Archive) for easy distribution and installation. In addition to providing this service, the phar extension also provides a file-format abstraction method for creating and manipulating tar and zip files through the PharData class, much as PDO provides a unified interface for accessing different databases. Unlike PDO, which cannot convert between different databases, Phar also can convert between tar, zip and phar file formats with a single line of code.