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

## Table of Contents

- Changes in reference handling
- Reading []
- Integer values in function parameters
- Class and object changes
- Extensions
- Date/time support
- Changes in database support
- Checking for E_STRICT

## 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.