Built-in modules are compiled directly into PHP and
carried around with every PHP process; their functionality is
instantly available to every script that's being run. Like
external modules, built-in modules have advantages and
disadvantages, as described in the following table:
Advantages | Disadvantages |
No need to load the module specifically; the functionality is instantly available. | Changes to built-in modules require recompiling of PHP. |
No external files clutter up the disk; everything resides in the PHP binary. | The PHP binary grows and consumes more memory. |