Unfortunately, relatively little information is available about writing efficient PHP applications -- hence the motivation for writing this tutorial. The following are some resources that I used in writing this tutorial.

• Visit the PHP Web site (http://www.php.net).
• If you have problems with a particular function, read the user-contributed notes and comments throughout the PHP manual (http://www.php.net/manual/en/). Chances are good that someone else has experienced the same problem and added notes about it to the manual.
• The article, Optimizing PHP Scripts suggests "programming time is expensive." Read how to improve the performance of your PHP applications from other angles. It also contains a couple of useful sections on when to optimize, and how to measure performance of pieces of your application.
• Check out Zend, the commercial side of PHP. It provides additional products that can help improve performance: Zend Cache and Zend Optimizer.
• See "Using Strings" on the Zend Web site for more information on the different uses of strings in PHP.
• Get further information on Internet Explorer's handling of MIME-types from Microsoft Support WebCast: MIME-Type Handling in Microsoft Internet Explorer, January 11, 2001. In particular, refer to the Questions & Answers section at the end of the Web cast where several questions address the possible need for two GET requests.
• Learn how to make your wireless content more dynamic with the use of PHP in the IBM developerWorks tutorial, Flex your PHP (developerWorks, March 2002).
• Visit Steven Gould's Web site and get the useful PHP Quick Reference Card.