PHP has already a long history behind him:
Legendary PHP 1.0, PHP/FI, PHP 3.0 and PHP 4.0.
Migrating from PHP 2 to PHP 3?
PHP/FI 2.0 is no longer supported. Please see
section for information about migration
from PHP/FI 2.0.
If you are still working with PHP 2, we
strongly recommend you
to upgrade straight to PHP 4.