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Originally, PHP was famous for interfacing with many different database systems, but it also has support for other external systems. Support comes in the form of modules called extensions. They either compile directly into PHP or are loaded dynami-cally. New extensions are added to the PHP project regularly. The extensions expose groups of functions for using these external systems. As mentioned, some of these are databases. PHP offers functions for talking natively with most popular database sys-tems, and it provides access to ODBC drivers. Other extensions give you the ability to send messages using a particular network protocol, such as LDAP or IMAP. These functions are described in detail in Part II. Because PHP developers are enthusiastic and industrious, you will undoubtedly find more extensions have been added since I wrote this.
Pspell is a system for checking spelling. An extension provides support for numbers of arbitrary precision. There is an extension for dealing with various calendar systems. An extension provides support for DBM-style databases. You can use the SNMP, IMAP, and LDAP protocols. The Interbase and Informix databases are supported natively, as are mSQL, MySQL, MS SQL, Sybase, Oracle, and PostgreSQL. You can also parse XML or create WDDX packets. You can even extract meta information about your digital pictures using the EXIF extension. At the time of writing, automated coffee making is not yet supported.The normal process a Web server goes through to deliver a page to a browser is as follows. It all begins when a browser makes a request for a Web page. Based on the URL, the browser resolves the address of the Web server, identifies the page it would like, and gives any other information the Web server may need. Some of this infor-mation is about the browser itself, like its name (Mozilla), its version (4.08), or the operating system (Linux). Other information given the Web server could include text the user typed into form fields.
If the request is for an HTML file, the Web server will simply find the file, tell the browser to expect some HTML text, and then send the contents of the file. The browser gets the contents and begins rendering the page based on the HTML code. If you have been programming HTML for any length of time, this will be clear to you.
Hopefully, you have also had some experience with CGI scripts. When a Web server gets a request for a CGI, it can't just send the contents of the file. It must execute the script first. The script will generate some HTML code, which then gets sent to the browser. As far as the browser is concerned, it's just getting HTML.
1.5 Hardware and Software Requirements When a PHP page is requested, it is processed exactly like a CGI, at least to the extent that the script is not simply sent to the browser. It is first passed through theOne great advantage of Open Source software is that it provides the opportunity for adaptation to new environments. This is true of PHP. Although originally intended as a module for the Apache Web server, PHP has since abstracted its Web server inter-face. The new abstraction layer allowed an ISAPI module to be written, which allows it to work equally well with Microsoft's Internet Information Server. With regard to hardware requirements, I have personally witnessed PHP running on 100-MHz Pen-tium machines running Slackware Linux and Windows NT respectively. Performance was fine for use as a personal development environment. That the engines for PHP 3 and 4 were developed on Intel 486 CPUs must have helped. A site expected to receive thousands of requests a day would need faster hardware, of course. Although more resources are needed when comparing a PHP-powered site to a flat HTML site, the requirements are not dramatically different. Despite my example, you are not limited to Intel hardware. PHP works equally well on PowerPC, Sparc, and other 32-bit or better CPUs.
When choosing an operating system, you have the general choice between Windows and a UNIX-like OS. PHP will run on older Windows operating systems, although these operating systems aren't suited for high-traffic Web servers. It will also run on Windows 2000 and Windows XP. For UNIX operating systems, PHP works well with Linux and Solaris as well as others. If you have chosen a PPC-based system, such as a Macintosh, you may choose LinuxPPC, a version of Linux. Chad Cunningham contributed patches for compiling PHP in Apple's OS X. There's even support of IBM's OS/ 2 and Novell Netware.
PHP still works best with the Apache Web server. But it now works very well with IIS. It also compiles as a module for the fhttpd Web server. You can make PHP work with almost any Web server using the CGI version, but I don't recommend this setup for production Web sites.
If you are using Linux, you can easily find an RPM for Apache and PHP, but this installation may not include every PHP feature you want. I recommend this route as a very quick start. You can always pursue compiling Apache and PHP from scratch later. PHP will compile on most versions of UNIX-like operating systems, including Solaris and Linux. If you have ever compiled software you've found on the Net, you will have little trouble with this installation. If you don't have experience extracting files from a tar archive and executing make files, you may wish to rely on your system administrator or someone else more experienced. You will need to have root privileges to completely install PHP.
The first step is to download the tar files and unpack them. Download the newest versions from the PHP site <http://www.php.net/downloads.php>and the Apache site <http://httpd.apache.org/>.At the time of writing, Apache 2 is considered stable. Support for mod_ phpin Apache is not complete. The following instructions assume Apache 1.3 and Apache 2 may require a few changes.
After unpacking the tar file, the first step is to configure Apache. This is done by running the configure script inside the Apache directory. Listing 1. 1 shows a minimal configuration.
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Created: March 27, 2003
Revised: Sept. 1, 2003
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