# Migrating from PHP 4 to PHP 5

## Table of Contents

- Backward Incompatible Changes
- CLI and CGI
- Migrating Configuration Files
- New Functions
- New Directives
- Databases
- New Object Model
- Error Reporting

## What has changed in PHP 5

PHP 5 and the integrated Zend Engine 2 have greatly improved PHP's performance and capabilities, but great care has been taken to break as little existing code as possible. So migrating your code from PHP 4 to 5 should be very easy. Most existing PHP 4 code should be ready to run without changes, but you should still know about the few differences and take care to test your code before switching versions in production environments.