Migrating from PHP 5.0.x to PHP 5.1.x
PHP Manual

Key PHP 5.1.x features

Some of the key features of PHP 5.1.x include:

  • A complete rewrite of date handling code, with improved timezone support.

  • Significant performance improvements compared to PHP 5.0.X.

  • PDO extension is now enabled by default.

  • Over 30 new functions in various extensions and built-in functionality.

  • Over 400 various bug fixes.