compiler ?

hi all: after experiencing the power of PHP 4.0 + zend I am wondering what does a "compiler" stand in the whole architecture. We are still writing scripts, aren't we ? I personnaly assumed that the compiler functions when a script is executed, like the JIT compiler tech in Java. is that so ? further, another thing that confuses me is that zend'll execute some machine independent intermediate codes in the future release. that means zend understands machine independent binary codes and scripts as well ? so what about the efficiency issue between the above two ? thanx in advance -- It's imagination which limits what we can program ! Douglas <douglas@inforian.com><ICQ:14397736>