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# Chapter 49. General Information

This section holds the most general questions about PHP: what it is and what it does.

1. What is PHP?
2. What does PHP stand for?
3. What is the relation between the versions?
4. Can I run several versions of PHP at the same time?
5. What are the differences between PHP 3 and PHP 4?
6. I think I found a bug! Who should I tell?

1. What is PHP?

From the preface of the manual:

PHP is an HTML-embedded scripting language. Much of its syntax is borrowed from C, Java and Perl with a couple of unique PHP-specific features thrown in. The goal of the language is to allow web developers to write dynamically generated pages quickly.

A nice introduction to PHP by Stig Sæther Bakken can be found at http://www.zend.com/zend/art/intro.php on the Zend website. Also, much of the PHP Conference Material is freely available.

2. What does PHP stand for?

PHP stands for PHP: Hypertext Preprocessor. This confuses many people because the first word of the acronym is the acronym. This type of acronym is called a recursive acronym. The curious can visit Free On-Line Dictionary of Computing for more information on recursive acronyms.

3. What is the relation between the versions?

PHP/FI 2.0 is an early and no longer supported version of PHP. PHP 3 is the successor to PHP/FI 2.0 and is a lot nicer. PHP 4 is the current generation of PHP, which uses the Zend engine under the hood. PHP 5 uses Zend engine 2 which, among other things, offers many additional OOP features.

4. Can I run several versions of PHP at the same time?

Yes. See the `INSTALL` file that is included in the PHP 4 source distribution. Also, read the related appendix.

5. What are the differences between PHP 3 and PHP 4?

There are a couple of articles written on this by the authors of PHP 4. 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

Please see the What's new in PHP 4 overview for a detailed explanation of these features and more. If you're migrating from PHP 3 to PHP 4, also read the related appendix.

6. I think I found a bug! Who should I tell?

You should go to the PHP Bug Database and make sure the bug isn't a known bug. If you don't see it in the database, use the reporting form to report the bug. It is important to use the bug database instead of just sending an email to one of the mailing lists because the bug will have a tracking number assigned and it will then be possible for you to go back later and check on the status of the bug. The bug database can be found at http://bugs.php.net/.

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