A browser is a software application that serves as the client portion of the World Wide Web (WWW). It makes it possible for users to download web pages and display them on their computer. Pages are stored on web servers that are either publicly available via the Internet or privately available via an intranet.
A web page is a document that is formatted using the HTML markup language (although other formatting languages are also supported). In addition to providing a formatting language, HTML provides the structure for embedding hyperlinks in documents. A hyperlink is a segment of the document that contains an embedded reference to another web page. If the hyperlink is text-based, it is typically displayed by the browser as underlined text and/or in an alternate color. A hyperlink may also be embedded in an image or even a video. When the cursor is placed over the hyperlink, the cursor changes to indicate the presence of the hyperlink (e.g., to a small pointing hand). If the user clicks on the hyperlink, the browser connects to the specified server and requests the specified web page.
The protocol a browser typically implements to download web pages is called the Hypertext Transfer Protocol (HTTP). Other protocols, however, can also be used (e.g., FTP). The web page a browser is to download is identified by its URL.
Although the HTML document is the primary type of document downloaded by HTTP and displayed on the browser, most browsers can also download and display many other file types, including images (e.g., JPG, GIF, PNG) and various specialized pages (e.g., ASP, CSS, etc.).
Although modern browsers come with significant basic capabilities, the power of these platforms can be greatly enhanced by the incorporation of plug-ins. A plug-in is a software module that can be added to a basic program to enhance it's functionality. Some of the more common plug-ins include Flash, Shockwave, and Java. Other plug-ins commonly found include bookmarking (e.g., Delicious), micro-blogging (Twitter), and web searching (Google toolbar), to name a few.
There have been many browsers since the early 1990s. Although there were browser-like applications as far back as the mid-1980s, the first modern browser with HTTP and HTML capabilities is thought to be the Mosaic browser developed by the National Center for Supercomputing Applications (NCSA) in 1992 and released to the general public in 1993. The NCSA, located at the University of Illinois, is one of the five original supercomputer centers funded by the National Science Foundation's (NSF) Supercomputer Centers Program. Since that initial launch, numerous browsers have emerged from a variety of sources. Although some of these succeeded initially, once Microsoft introduced Windows Internet Explorer (IE), most struggled to compete with the dominance of a browser bundled with the native operating system found on most desktop systems.
Other browsers that have been introduced over time include:
- AOL Explorer (powered by Internet Explorer)
- Chrome from Google
- Epiphany from Gnome
- Firefox from Mozilla
- Navigator from Netscape
- Opera from Opera Software
- Safari from Apple
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