The Advantage Of PHP

First, PHP have a unique structure, base on "share nothing" philosophy, each thread run  php web server and Zend Engine was done independently, completely freeing resources after the end of the task .This help PHP what is dinamic language and interpreter but with very fast performance, and especially, consuming very little resources. Another point is the HTTP protocol (communication protocol of the web) also operates a similar "HTTP, each request is distinct".

Second, PHP  was born to code web (see more) so designers of PHP will certainly better than other languages in web technology. PHP itself is a very powerful template engine friendly web (HTML-CSS-JavaScript).

Third, PHP is the language used for the world's most popular web, almost web hosts support PHP.  PHP also offers a number of web developers the world's largest which has built a large community, a lot bigger than other communities.

Read more reviews on TIOBE community, PHP 5th, high over a language used only Web - server side scripts.

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Fourth, PHP is open source language, so with millions of apps available, free, open source library enables programming language becomes quick and quality.
If there are 1-2 other languages eg ASP.NET product has a - two products, the PHP forum has a few dozen products have much better quality .Can see the same thing over other apps such as: Shopping, Shopping Cart, CMS.
The PHP library technology more than any other web programming, contributed by a broad community, including leading IT companies such as Oracle, Yahoo, IBM, Zend, FaceBook ...

Fifth, With open source stack LAMP technologies including the Linux operating system, Apache Web server, System Administrator Mysql database and PHP. Made a powerful open platform with a very modest cost. But easily extended.