PHP has already a long history behind him: Legendary PHP 1.0, PHP/FI, PHP 3.0 and PHP 4.0.
1. Migrating from PHP 2 to PHP 3?
PHP/FI 2.0 is no longer supported. Please see appropriate manual 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.