Web Browser

A Web browser is a software application which enables a user to display and interact with text, images, videos, music, games 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 site. 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 format HTML information for display, so the appearance of a Web page may differ between browsers.

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.

HISTORY
The history of the Web browser dates back to late 1980s, when a variety of technologies laid the foundation for the first Web browser, the WorldWideWeb, by Tim Berners-Lee in 1991. That browser brought together a variety of existing and new software and hardware technologies.

Over the following years, Web browsers were introduced by companies like Mozilla, Netscape, Microsoft, Apple, and Opera. More recently, Google entered the browser market.

CURRENT WEB BROWSERS
Some of the Web browsers currently available for personal computers include Internet Explorer, Mozilla Firefox, Safari, Opera, Avant Browser, Konqueror, Lynx, Google Chrome, Maxthon, Flock, Arachne, Epiphany, K-Meleon and AOL Explorer.

PROTOCOLS & STANDARDS
Web browsers communicate with Web servers primarily using Hypertext Transfer Protocol (HTTP) 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 version of 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, RFC 1738), which is treated as an address, beginning with http: for HTTP transmission.

Many browsers also support a variety of other URL types and their corresponding protocols, such as gopher: for Gopher (a hierarchical hyperlinking protocol), ftp: for File Transfer Protocol (FTP), rtsp: for Real-time Streaming Protocol (RTSP), and https: for HTTPS (HTTP Secure, which is HTTP augmented by Secure Sockets Layer or Transport Layer Security).

The file format for a Web page is usually HTML (HyperText 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 a combination of standards-based and de facto HTML and XHTML, which should be rendered in the same way by all browsers.
No browser fully supports HTML 4.01, XHTML 1.x or CSS 2.1 yet. Many sites are designed using WYSIWYG HTML-generation programs such as Adobe Dreamweaver or Microsoft FrontPage.

Microsoft FrontPage often generates non-standard HTML by default, hindering the work of the W3C in promulgating standards, specifically with XHTML and Cascading Style Sheets (CSS), which are used for page layout.
Dreamweaver and other more modern Microsoft HTML development tools such as Microsoft Expression Web and Microsoft Visual Studio conform to the W3C standards.

Some of the more popular browsers include additional components to support Usenet news, Internet Relay Chat (IRC), and e-mail. Protocols supported may include Network News Transfer Protocol (NNTP), Simple Mail Transfer Protocol (SMTP), Internet Message Access Protocol (IMAP), and Post Office Protocol (POP).
These browsers are often referred to as "Internet suites" or "application suites" rather than merely Web browsers.


Source: en.wikipedia.org