php-doc-en/chapters/intro.xml

 <chapter id="introduction">
  <title>Introduction</title>

  <sect1 id="intro-whatis">
   <title>What is PHP?</title>
   <simpara>
    PHP (officially "PHP: Hypertext Preprocessor") is a server-side
    HTML-embedded scripting language.
   </simpara>
   <para>
    Simple answer, but what does that mean? An example:
   </para>
   <para>
    <example>
     <title>An introductory example</title>
     <programlisting>
&lt;html>
    &lt;head>
        &lt;title>Example&lt;/title>
    &lt;/head>
    &lt;body>
        &lt;?php echo "Hi, I'm a PHP script!"; ?>
    &lt;/body>
&lt;/html>
     </programlisting>
    </example>
   </para>
   <para>
    Notice how this is different from a CGI script written in other
    languages like Perl or C -- instead of writing a program with lots
    of commands to output HTML, you write an HTML script with a some
    embedded code to do something (in this case, output some
    text). The PHP code is enclosed in special <link
    linkend="language.basic-syntax.phpmode">start and end tags</link>
    that allow you to jump into and out of PHP mode.
   </para>
   <para>
    What distinguishes PHP from something like client-side Javascript
    is that the code is executed on the server. If you were to have a
    script similar to the above on your server, the client would receive
    the results of running that script, with no way of determining what
    the underlying code may be. You can even configure your web server
    to process all your HTML files with PHP, and then there's really no
    way that users can tell what you have up your sleeve.
   </para>
  </sect1>

  <sect1 id="intro-whatcando">
   <title>What can PHP do?</title>
   <para>
    At the most basic level, PHP can do anything any other CGI
    program can do, such as collect form data, generate dynamic
    page content, or send and receive cookies.
   </para>
   <para>
    Perhaps the strongest and most significant feature in PHP is its
    support for a wide range of databases. Writing a database-enabled
    web page is incredibly simple.  The following databases are currently
    supported:
    <blockquote>
     <simplelist columns="3">
      <member>Adabas D</member>
      <member>dBase</member>
      <member>Empress</member>
      <member>FilePro</member>
      <member>Informix</member>
      <member>InterBase</member>
      <member>mSQL</member>
      <member>MySQL</member>
      <member>Oracle</member>
      <member>PostgreSQL</member>
      <member>Solid</member>
      <member>Sybase</member>
      <member>Velocis</member>
      <member>Unix dbm</member>
     </simplelist>
    </blockquote>
   </para>
   <para>
    PHP also has support for talking to other services using protocols
    such as IMAP, SNMP, NNTP, POP3, or even HTTP. You can also open raw
    network sockets and interact using other protocols.
   </para>
   <figure>
    <title>Internal Structure</title>
    <graphic fileref="../images/php3_internal_structure.gif"/>
   </figure>
   <figure>
    <title>Request Scheme</title>
    <graphic fileref="../images/php3_request_scheme.gif"/>
   </figure>
  </sect1>

  <sect1 id="intro-history">
   <title>A brief history of PHP</title>
   <simpara>
    PHP was conceived sometime in the fall of 1994 by &link.rasmus;.
    Early non-released versions were used on his home page to keep
    track of who was looking at his online resume.  The first version
    used by others was available sometime in early 1995 and was known
    as the Personal Home Page Tools.  It consisted of a very
    simplistic parser engine that only understood a few special macros
    and a number of utilities that were in common use on home pages
    back then.  A guestbook, a counter and some other stuff.  The
    parser was rewritten in mid-1995 and named PHP/FI Version 2.  The
    FI came from another package Rasmus had written which interpreted
    html form data.  He combined the Personal Home Page tools scripts
    with the Form Interpreter and added mSQL support and PHP/FI was
    born.  PHP/FI grew at an amazing pace and people started
    contributing code to it.
   </simpara>
   <simpara>
    It is difficult to give any hard statistics, but it is estimated
    that by late 1996 PHP/FI was in use on at least 15,000 web sites
    around the world.  By mid-1997 this number had grown to over
    50,000.  Mid-1997 also saw a change in the development of PHP.  It
    changed from being Rasmus' own pet project that a handful of
    people had contributed to, to being a much more organized team
    effort. The parser was rewritten from scratch by Zeev Suraski and
    Andi Gutmans and this new parser formed the basis for PHP Version
    3.  A lot of the utility code from PHP/FI was ported over to PHP3
    and a lot of it was completely rewritten.
   </simpara>
   <simpara>
    Today (end-1999) either PHP/FI or PHP3 ships with a number of
    commercial products such as C2's StrongHold web server and RedHat
    Linux. A conservative estimate based on an extrapolation from
    numbers provided by <ulink url="&url.netcraft;">NetCraft</ulink>
    (see also <ulink url="&url.netcraft-survey;">Netcraft Web Server
    Survey</ulink>) would be that PHP is in use on over 1,000,000
    sites around the world.  To put that in perspective, that is more
    sites than run Netscape's flagship Enterprise server on the
    Internet.
   </simpara>
   <figure>
    <title>NetCraft Webserver Survey</title>
    <graphic fileref="../images/phpstats-199911.gif"/>
   </figure>
   <simpara>
    Also as of this writing, work is underway on the next generation
    of PHP, which will utilize the powerful <ulink
    url="&url.zend;">Zend</ulink> scripting engine to deliver higher
    performance, and will also support running under webservers other
    than Apache as a native server module.
   </simpara>
  </sect1>

 </chapter>

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