Browser Definition

A web browser, commonly referred to as just a browser, is a type of program that is used on computers, and increasingly on other devices as well, to locate, display and interact with web pages and other resources on the Internet.

Browsers can also be used to access resources on other types of networks, including local area networks (LANs) and home networks, as well as on the same computer on which the browser is running. In addition to computers, browsers can also operate on some cell phones, personal digital assistants (PDAs) and industrial controls.

The content accessed by browsers on the Web is generally hosted on specialized computers called web servers. Browsers send user requests to these servers and fetch web pages from them primarily through the use of HTTP (hypertext transfer protocol). The most commonly employed version of HTTP is HTTP/1.1.

Any web page is located by means of its URL (uniform resource locator), which is its address on the Internet. After a user types a URL into the space in the location bar near the top of the browser or clicks on a hyperlink1, this request is routed through the Internet via specialized computers called routers until it reaches the web server that is hosting the desired page.

The file format for a web page is usually HTML (hyper-text markup language) and is identified in the HTTP protocol using a MIME (multipurpose Internet mail extensions) content type. Most browsers natively support a variety of file formats in addition to HTML, such as the JPEG, GIF and PNG image formats, and can be extended to support additional formats, including those for sound and video, through the use of optional plug-ins.

The most popular web browser is still Microsoft's Internet Explorer. However, its market share has been declining because of the failure of that company to update it for a number of years and the emergence of competitive browsers with useful new features and greatly improved performance. The fastest growing browser in terms of market share is Firefox, which is free software and a descendant of the once dominant Netscape browser. Others include Safari, which was developed by Apple Computer and is only available for the Macintosh, and Opera2.

Among the most important of the new features pioneered by these new browsers is tabbed browsing. This allows a number of web pages to be open simultaneously in a single browser window, and the user can switch among these pages instantaneously by clicking on their tabs. In addition to making it easy for users to switch among pages and compare their contents, this also has the effect of speeding up downloading of pages by allowing a page in one tab to be read while pages in other tabs are being downloaded.

Another advantage of these newer browsers is that they are much more compliant with industry-wide Web standards, including HTTP/1.1 and CSS (cascading style sheets). Standards compliance makes it much easier to design web pages and also allows pages to be rendered (i.e., converted to its final form to be viewed by users) in browsers more reliably and consistently. In addition, versions of Firefox and Opera are available for various operating systems, whereas Internet Explorer can only run on Microsoft Windows.

The newer browsers also feature faster downloading speeds and greatly enhanced security. The latter includes increased resistance to infection by computer viruses and other malware as well as providing warnings about phishing (i.e., counterfeit pages designed to extract personal data from users).

The first browser, which was called Silversmith and was written by John Bottoms in 1987 (before the birth of the Web), was intended for accessing SGML (standardized general markup language) documents. The first web browser, named WorldWideWeb, was developed during the latter half of 1990 by Tim Berners-Lee, a physicist by training and the founder of the Web. Berners-Lee, also created the first web server, the first web page, URLs and the first versions of HTML and HTTP. He designed HTML as a highly simplified form of SGML (which is very complex and requires specialized training to be able to work with it) so that it would be easy for ordinary people to create web pages and in order to simplify the development of web browsers and web servers.

Berners-Lee's browser was soon followed by others, including Mosaic, which was developed at the National Center for Supercomputing Applications (NCSA) beginning in 1992 and released in 1993. Mosaic was the first browser that ran on Microsoft Windows (rather than UNIX), and it played a key role in making the Web easily accessible to the general public.

1There are other ways that a browser can send a request to a web server, including redirects, automatic page reloadings and data automatically sent to provide information about the browser and the computer on which it is running.

2Firefox can be downloaded from the Internet at Opera can be downloaded at

Created December 4, 2006.
Copyright © 2006 The Linux Information Project. All Rights Reserved.