PHP's structure is heavily influenced by the C programming language, a general-purpose language that has existed since 1978 and has been used to develop many large programs, including UNIX and Microsoft Windows. C's popularity led many subsequent languages to use its same general syntax, so that programmers familiar with C would quickly feel comfortable using the new language instead. Other C-based languages include C++, Java, Perl, JavaScript, and C#. Of course, all are fairly distinct languages, but since all of these languages have a similar core, you will find them fairly familiar after seeing PHP.
PHP development is continuing, as those on the PHP team refine the language to enhance its security, to facilitate development of large-scale Web sites, and provide other new features. As of mid-2007, when this was written, the current official version of PHP is version 5, although version 6 is nearing completion. Version 4 is still in wide use, partially because people haven't gotten around to installing the newer versions — but also because established Web sites need to take issues like security and reliability very seriously, and version 4 is a more thoroughly tested software package
