Just because Linux is distributed for free, it doesn’t mean the software is not copyrighted. Linux has been registered as copyrighted under the GNU General Public License (GPL), which is known in the programming community as a copyleft instead of copyright because of its nature. The GPL allows you to redistribute the Linux software, along with the complete source code, to anyone who wants it. However, the original owner of the components retains the copyrights to the software.

In 1994, an incredibly forward-thinking man named Rasmus Lerdorf developed a set of tools that used a parsing engine to interpret a few macros here and there. They were not extravagant: a guest book, a counter, and some other "home page" elements that were cool when the Web was in its infancy. He eventually combined these tools with a form interpretation (FI) package he had written, added some database support, and released what was known as PHP/FI.Then, in the spirit of Open Source software development, developers all over the world began contributing to PHP/FI. By 1997, more than 50,000 Web sites were using PHP/FI to accomplish different tasks— connecting to a database, displaying dynamic content, and so on.

Every Window object has a document property that refers to a Document object. The Document object is arguably more important than the Window object itself: while the Window represents the browser window, the Document object represents the HTML document that is displayed in that window. The Document object has various properties that refer to other objects which allow access to and modification of document content. The way that document content is accessed and modified is called the document object model, or DOM, and there are several DOMs in existence:

Datacenter Edition builds on the feature set offered by Enterprise Edition and eliminates a few features that aren’t considered appropriate for a large enterprise data center. For example, Datacenter does not support the Internet Connection Firewall or Internet Connection Sharing, two features designed to make Windows an Internet gateway for network clients. Both features are, however, supported by Standard Edition and Enterprise Edition. Datacenter Edition adds support for up to 64GB of server RAM and up to 32-way processor support. These features require a specialized Hardware Abstraction Layer (HAL), which is provided by the server hardware manufacturer. Datacenter Edition’s Cluster Service supports eight-way clusters, enabling you to build more complex failover clusters for mission-critical applications.