Web browser

An example of a web browser (Mozilla Firefox running under Microsoft Windows).

A Web browser is a software application that enables a user to display and interact with text, images, and other information typically located on a Web page at a Web site on the World Wide Web or a local area network. Text and images on a Web page can contain hyperlinks to other Web pages at the same or different Web sites. Web browsers allow a user to quickly and easily access information provided on many Web pages at many Web sites by traversing these links.

Web browsers available for personal computers include Microsoft Internet Explorer, Mozilla Firefox, Apple Safari, Netscape, and Opera, in order of descending popularity (July 2006). Web browsers are the most commonly used type of HTTP user agent. Although browsers are typically used to access the World Wide Web, they can also be used to access information provided by Web servers in private networks or content in file systems.

Protocols and standards

Web browsers communicate with Web servers primarily using HTTP (hypertext transfer protocol) to fetch Web pages. HTTP allows Web browsers to submit information to Web servers as well as fetch Web pages from them. The most commonly used HTTP is HTTP/1.1, which is fully defined in RFC 2616. HTTP/1.1 has its own required standards that Internet Explorer does not fully support, but most other current-generation Web browsers do.

Pages are located by means of a URL (uniform resource locator), which is treated as an address, beginning with http: for HTTP access. Many browsers also support a variety of other URL types and their corresponding protocols, such as ftp: for FTP (file transfer protocol), rtsp: for RTSP (real-time streaming protocol), and https: for HTTPS (an SSL encrypted version of HTTP).

The file format for a Web page is usually HTML (hyper-text markup language) and is identified in the HTTP protocol using a MIME content type. Most browsers natively support a variety of formats in addition to HTML, such as the JPEG, PNG and GIF image formats, and can be extended to support more through the use of plugins. The combination of HTTP content type and URL protocol specification allows Web page designers to embed images, animations, video, sound, and streaming media into a Web page, or to make them accessible through the Web page.

Early Web browsers supported only a very simple version of HTML. The rapid development of proprietary web browsers led to the development of non-standard dialects of HTML, leading to problems with Web interoperability. Modern Web browsers support standards-based HTML and XHTML, which should display in the same way across all browsers. Internet Explorer does not fully support HTML 4.01 and XHTML 1.x yet. Currently many sites are designed using WYSIWYG HTML generation programs such as Macromedia Dreamweaver or Microsoft Frontpage. These often generate non-standard HTML by default, hindering the work of the W3C in developing standards, specifically with XHTML and CSS (cascading style sheets, used for page layout).

Some of the more popular browsers include additional components to support Usenet news, IRC (Internet relay chat), and e-mail. Protocols supported may include NNTP (network news transfer protocol), SMTP (simple mail transfer protocol), IMAP (Internet message access protocol), and POP (post office protocol). These browsers are often referred to as Internet suites or application suites rather than merely web browsers.

Brief history

A NeXTcube was used by Tim Berners-Lee (who pioneered the use of hypertext for sharing information) as the world's first Web server, and also to write the first Web browser, WorldWideWeb in 1990. Berners-Lee introduced it to colleagues at CERN in March 1991. Since then the development of Web browsers has been inseparably intertwined with the development of the Web itself.

An early popular Web browser was ViolaWWW, which was modeled after HyperCard. However, the explosion in popularity of the Web was triggered by NCSA Mosaic which was a graphical browser running originally on Unix but soon ported to the Apple Macintosh and Microsoft Windows platforms. Version 1.0 was released in September 1993, and was dubbed the killer application of the Internet. Marc Andreessen, who was the leader of the Mosaic team at NCSA, quit to form a company that would later be known as Netscape Communications Corporation.

Netscape released its flagship Navigator product in October 1994, and it took off the next year. Microsoft, which had thus far not marketed a browser, now entered the fray with its Internet Explorer product, purchased from Spyglass Inc. This began what is known as the browser wars, the fight for the web browser market between Microsoft and Netscape.

The wars put the web in the hands of millions of ordinary PC users, but showed how commercialization of the web could stymie standards efforts. Both Microsoft and Netscape liberally incorporated proprietary extensions to HTML in their products, and tried to gain an edge by product differentiation. Starting with the acceptance of the Microsoft proposed Cascading Style Sheets over Netscape's JavaScript Style Sheets (JSSS) by W3C, the Netscape browser started being generally considered inferior to Microsoft's browser version after version, from feature considerations to application robustness to standard compliance. The wars effectively ended in 1998 when it became clear that Netscape's declining market share trend was irreversible. This trend may have been due in part to Microsoft's integrating its browser with its operating system and bundling deals with OEMs; Microsoft faced antitrust litigation on these charges.

Netscape responded by open sourcing its product, creating Mozilla. This did nothing to slow Netscape's declining market share. The company was purchased by America Online in late 1998. At first, the Mozilla project struggled to attract developers, but by 2002 it had evolved into a relatively stable and powerful internet suite. Mozilla 1.0 was released to mark this milestone. Also in 2002, a spin off project that would eventually become the popular Mozilla Firefox was released. In 2004, Firefox 1.0 was released; Firefox 1.5 was released in December 2005. Firefox 2 is planned to be released in late 2006 and work has already begun on Firefox 3 which is scheduled for release in 2007. As of 2005, Mozilla and its derivatives account for approximately 10% of Web traffic.

Opera, an innovative, speedy browser popular in handheld devices, particularly mobile phones, as well as on PCs in some countries was released in 1996 and remains a niche player in the PC Web browser market.

The Lynx browser remains popular for Unix shell users and with vision impaired users due to its entirely text-based nature. There are also several text-mode browsers with advanced features, such as w3m, Links and the Links forks such as ELinks.

While the Macintosh scene too has traditionally been dominated by Internet Explorer and Netscape, the future appears to belong to Apple's Safari which is based on Apple's WebKit layout engine, derived from the KHTML layout engine of the open source Konqueror browser. Safari is the default browser on Mac OS X.

In 2003, Microsoft announced that Internet Explorer would no longer be made available as a separate product but would be part of the evolution of its Windows platform, and that no more releases for the Macintosh would be made. However, more recently in early 2005, Microsoft changed its plans and announced that version 7 of Internet Explorer would be released for its Windows XP and Windows Server 2003 operating systems in addition to the upcoming "Windows Vista" operating system.

Features

Different browsers can be distinguished from each other by the features they support. Modern browsers and Web pages tend to utilize many features and techniques that did not exist in the early days of the Web. As noted earlier, with the browser wars there was a rapid and chaotic expansion of browser and World Wide Web feature sets.

The following is a list of some of the most notable features: