Sometimes, PHP "as is" simply isn't enough. Although
these cases are rare for the average user, professional
applications will soon lead PHP to the edge of its
capabilities, in terms of either speed or functionality.
New functionality cannot always be implemented natively
due to language restrictions and inconveniences that
arise when having to carry around a huge library of
default code appended to every single script, so another
method needs to be found for overcoming these eventual
lacks in PHP.
As soon as this point is reached, it's time to touch
the heart of PHP and take a look at its core, the C code
that makes PHP go.