A web browser (commonly referred to as a browser)
is a
software application for retrieving, presenting and
traversing information resources on the
World Wide Web. An information resource is identified
by a
Uniform Resource Identifier (URI) and may be a
web page, image, video or other piece of content.[1]
Hyperlinks present in resources enable users easily to
navigate their
browsers to related resources.
Although browsers are primarily intended to use the World
Wide Web, they can also be used to access information provided
by
web servers in
private networks or files in
file systems. The major web browsers are
Google Chrome,
Firefox,
Internet Explorer,
Opera, and
Safari.[2]
History
The first web browser was invented in 1990 by Sir
Tim Berners-Lee. It was called
WorldWideWeb and was later renamed Nexus.[3]
In 1993, browser software was further innovated by
Marc Andreessen with the release of
Mosaic (later
Netscape), "the world's first popular browser",[4]
which made the World Wide Web system easy to use and more
accessible to the average person. Andreesen's browser sparked
the internet boom of the 1990s.[4]
The introduction of Mosaic in 1993 – one of the first graphical
web browsers – led to an explosion in web use. Andreessen, the
leader of the Mosaic team at NCSA, soon started his own company,
named
Netscape, and released the Mosaic-influenced
Netscape Navigator in 1994, which quickly became the world's
most popular browser, accounting for 90% of all web use at its
peak (see
usage share of web browsers).
Microsoft responded with its
Internet Explorer in 1995, also heavily influenced by
Mosaic, initiating the industry's first
browser war. Bundled with
Windows, Internet Explorer gained dominance in the web
browser market; Internet Explorer usage share peaked at over 95%
by 2002.[5]
Opera debuted in 1996; it has never achieved widespread use,
having less than 2% browser usage share as of February 2012
according to Net Applications.[7]
Its Opera-mini version has an additive share, in April 2011
amounting to 1.1% of overall browser use, but focused on the
fast-growing mobile phone web browser market, being preinstalled
on over 40 million phones. It is also available on several other
embedded systems, including
Nintendo's
Wii
video game console.
In 1998, Netscape launched what was to become the
Mozilla Foundation in an attempt to produce a competitive
browser using the
open source software model. That browser would eventually
evolve into
Firefox, which developed a respectable following while still
in the
beta stage of development; shortly after the release of
Firefox 1.0 in late 2004, Firefox (all versions) accounted for
7% of browser use.[5]
As of August 2011, Firefox has a 28% usage share.[7]
Apple's
Safari had its first beta release in January 2003; as of
April 2011, it had a dominant share of Apple-based web
browsing, accounting for just over 7% of the entire browser
market.[7]
The most recent major entrant to the browser market is
Chrome, first released in September 2008. Chrome's take-up
has increased significantly year by year, by doubling its usage
share from 8% to 16% by August 2011. This increase seems largely
to be at the expense of Internet Explorer, whose share has
tended to decrease from month to month.[8]
In December 2011, Chrome overtook
Internet Explorer 8 as the most widely used web browser but
still has lower usage than all versions of Internet Explorer
combined.[9]
Function
The primary purpose of a web browser is to bring information
resources to the user ("retrieval" or "fetching"), allowing them
to view the information ("display", "rendering"), and then
access other information ("navigation", "following links").
This process begins when the user inputs a
Uniform Resource Locator (URL), for example
http://en.wikipedia.org/, into the browser. The prefix of
the URL, the Uniform Resource Identifier or
URI, determines how the URL will be interpreted. The most
commonly used kind of URI starts with http: and
identifies a resource to be Retrieved over the
Hypertext Transfer Protocol (HTTP).[10]
Many browsers also support a variety of other prefixes, such as
https: for
HTTPS, ftp: for the
File Transfer Protocol, and file: for
local files. Prefixes that the web browser cannot directly
handle are often handed off to another application entirely. For
example, mailto: URIs are usually passed to the user's
default e-mail application, and news: URIs are passed to
the user's default newsgroup reader.
In the case of http, https, file, and
others, once the resource has been Retrieved the web browser
will display it.
HTML
and associated content (image files, formatting information such
as
CSS, etc.) is passed to the browser's
layout engine to be transformed from
markup to an interactive document, a process known as
"rendering". Aside from HTML, web browsers can generally display
any kind of content that can be part of a web page. Most
browsers can display images, audio, video, and
XML
files, and often have
plug-ins to support
Flash applications and
Java applets. Upon encountering a file of an unsupported
type or a file that is set up to be downloaded rather than
displayed, the browser prompts the user to save the file to
disk.
Information resources may contain
hyperlinks to other information resources. Each link
contains the URI of a resource to go to. When a link is clicked,
the browser navigates to the resource indicated by the link's
target URI, and the process of bringing content to the user
begins again.
Features
Available web browsers range in features from minimal,
text-based user interfaces with bare-bones support for HTML to
rich user interfaces supporting a wide variety of file formats
and protocols. Browsers which include additional components to
support e-mail,
Usenet news, and
Internet Relay Chat (IRC), are sometimes referred to as "Internet
suites" rather than merely "web browsers".[11][12][13]
All major web browsers allow the user to open multiple
information resources at the same time, either in different
browser windows or in different
tabs of the same window. Major browsers also include
pop-up blockers to prevent unwanted windows from "popping
up" without the user's consent.[14][15][16][17]
Most web browsers can display a list of web pages that the
user has
bookmarked so that the user can quickly return to them.
Bookmarks are also called "Favorites" in
Internet Explorer. In addition, all major web browsers have
some form of built-in
web feed
aggregator. In
Firefox, web feeds are formatted as "live bookmarks" and
behave like a folder of bookmarks corresponding to recent
entries in the feed.[18]
In
Opera, a more traditional feed reader is included which
stores and displays the contents of the feed.[19]
Furthermore, most browsers can be extended via
plug-ins, downloadable components that provide additional
features.
User interface
Some home media devices now include web browsers,
like this
LG Smart TV. The browser is controlled using an
on-screen keyboard and LG's "Magic Motion" remote.
Most major web browsers have these user interface elements in
common:[20]
- Back and forward buttons to go back to the
previous resource and forward respectively.
- A refresh or reload button to reload the
current resource.
- A stop button to cancel loading the resource. In
some browsers, the stop button is merged with the reload
button.
- A home button to return to the user's
home page.
- An
address bar to input the
Uniform Resource Identifier (URI) of the desired
resource and display it.
- A search bar to input terms into a
search engine. In some browsers, the search bar is
merged with the address bar.
- A
status bar to display progress in loading the resource
and also the URI of links when the cursor hovers over them,
and
page zooming capability.
Major browsers also possess
incremental find features to search within a web page.
Privacy
and security
Most browsers support
HTTP Secure and offer quick and easy ways to delete the web
cache,
cookies, and browsing history. For a comparison of the
current security vulnerabilities of browsers, see
comparison of web browsers.
Standards
support
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 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.
Extensibility
A
browser extension is a computer program that extends the
functionality of a web browser. Every major web browser supports
the development of browser extensions.
See also
References
External links