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What are the differences between PHP 3 and PHP 4? -- What are the differences between PHP 3 and PHP 4?There are a couple of articles written on this by the authors of PHP4. Here's a list of some of the more important new features:
Extended API module.
Generalized build process under UNIX
Generic web server interface that also supports multi-threaded web servers
Improved syntax highlighter
Native HTTP session support
Output buffering support
More powerful configuration system
Reference counting