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.