PHP version difference

　PHP1

　PHP originally appeared as a fast, practical toolkit. In 1994, in order to add a small and practical visitor tracking system to his website, Rasmus Lerdorf wrote a prototype of PHP. This is a simple tool wrapped in Perl. Because the usage effect was not ideal, Rasmus rewrote the tool in C language.

Later, more people noticed this lightweight and simple program and asked for more features. Rasmus decided to release a complete version, naming it Personal Home Page Tools. Later, Rasmus released a tool called FI that can perform SQL queries.

　PHP2

　In 1996, Rasmus released PHP/FI2.0, which is a basically complete PHP package. Not only can it access databases, but it can also be embedded in HTML pages. At this time, PHP/FI2.0 attracted a large number of program developers. Among the many programmers were Zeev Suraski and Andi Gutmans, who were later the founders of PHP3. Not satisfied with PHP/FI's performance in large projects, Zeev and Andi made significant improvements.

　PHP3

　At the end of 1998, the first official version of PHP3 was released, which featured better execution and a clearer structure. In addition, the powerful function of PHP3 lies in its scalability. In addition to providing end users with the infrastructure of databases, protocols, and APIs, its extensibility has attracted a large number of developers to join and submit new modules.

This brand new language is released with a new name. This name has a broader meaning than just the concept of "personal homepage tool". It is named with the simple abbreviation "PHP". This is a recursive abbreviation, and its full name is - PHP: Hypertext Preprocessor.

Soon, Zeev Suraski and Andi Gutmans invested in the development of new PHP. The design goal is to enhance program running performance and the modularity of PHP's own code.

　 PHP4

　 The new PHP core was called the "Zend" (named after Zeev and Andi) engine, which was released in May 2000 with the new version of PHP4.0. The performance of PHP4 has been significantly improved compared to PHP3. When the same script is run in PHP4, the performance can be improved by nearly 10 times. And the script optimizer provided by Zend can convert the source program into binary compiled code, which not only improves performance, but also protects the program source code from being exposed.

　 Added support for various web servers (such as Apache, IIS/PWS, OmniHTTPd, etc.) in PHP4. In addition, PHP4 also adds some new language features, such as rich array operation functions, complete session mechanism, support for output caching, etc. PHP4 also provides extended support for some cross-platform technologies, such as support for Adobe PDF, SWF, Java, Microsoft.NET and other technologies.

　 PHP4 also adds support for class objects. Although PHP4 is not perfect in this regard, it still greatly improves its support for object-oriented programming. The Pear library (PHP Extension and Application Repository) in PHP4 is the best example of object-oriented application and practice.

　PHP5

Although PHP4 is developing so rapidly, it still lacks some key features compared to other popular development languages. For example, the object-oriented functions in PHP4 are not perfect and exceptions cannot be implemented ( Exception) capture and processing. Therefore, we are still stretched in dealing with some special issues.

In July 2004, the release of the official version of PHP5 marked the arrival of a new PHP era. At its core is the second-generation Zend engine, which introduces support for the new PECL module. The biggest feature of PHP5 is that it introduces all object-oriented mechanisms and retains downward compatibility. Programmers no longer have to write classes that lack functionality and can implement class protection in a variety of ways. In addition, there are no longer problems with the integration of objects. Using PHP5 introduces type hints and exception handling mechanisms, which can handle and avoid errors more effectively.