Description:

The ClassLoader Component loads your project classes automatically if they
follow some standard PHP conventions.

Whenever you use an undefined class, PHP uses the autoloading mechanism
to delegate the loading of a file defining the class. Symfony provides
a "universal" autoloader, which is able to load classes from files that
implement one of the following conventions:
* The technical interoperability standards [1] for PHP 5.3 namespaces
and class names
* The PEAR naming convention [2] for classes

If your classes and the third-party libraries you use for your project follow
these standards, the Symfony autoloader is the only autoloader you will ever
need.

Optional: APC, XCache

[1] http://symfony.com/PSR0
[2] http://pear.php.net/manual/en/standards.php