Table of Contents
- Key PHP 5.1.x features
- Changes in reference handling
- Reading 
- Integer values in function parameters
- Class and object changes
- Date/time support
- Changes in database support
- Checking for E_STRICT
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.
Migrating from PHP 5.0.x to PHP 5.1.x