protocol that is run "on top of" (figuratively) the Internet, helping it to make it more functional. The advent of the
Mosaic web browser helped to make the web much more usable, including the display of images and moving images (
GIFs). The terms
Internet and
World Wide Web are often used without much distinction. However, the two terms do not mean the same thing. The Internet is a global system of
computer networks interconnected through telecommunications and
optical networking. In contrast, the World Wide Web is a global collection of documents and other
resources, linked by hyperlinks and
URIs. Web resources are accessed using
HTTP or
HTTPS, which are application-level Internet protocols that use the Internet transport protocols. The following example demonstrates the functioning of a web browser when accessing a page at the URL . The browser resolves the server name of the URL () into an
Internet Protocol address using the globally distributed
Domain Name System (DNS). This lookup returns an IP address such as
203.0.113.4 or
2001:db8:2e::7334. The browser then requests the resource by sending an
HTTP request across the Internet to the computer at that address. It requests service from a specific TCP port number that is well known for the HTTP service, so that the receiving host can distinguish an HTTP request from other network protocols it may be servicing. HTTP normally uses
port number 80 and, for HTTPS, it normally uses
port number 443. The content of the HTTP request can be as simple as two lines of text: GET /home.html HTTP/1.1 Host: example.org The computer receiving the HTTP request delivers it to the web server software listening for requests on port 80. If the web server can fulfil the request, it sends an HTTP response back to the browser indicating success: HTTP/1.1 200 OK Content-Type: text/html; charset=UTF-8 Followed by the content of the requested page. Hypertext Markup Language (
HTML) for a basic web page might look like this: Example.org – The World Wide Web The World Wide Web, abbreviated as WWW and commonly known ... The web browser
parses the HTML and interprets the markup (, for paragraph, and such) that surrounds the words to format the text on the screen. Many web pages use HTML to reference the URLs of other resources such as images, other embedded media,
scripts that affect page behaviour, and
Cascading Style Sheets that affect page layout. The browser makes additional HTTP requests to the web server for these other
Internet media types. As it receives its content from the web server, the browser progressively
renders the page onto the screen as specified by its HTML and these additional resources.
HTML Hypertext Markup Language (HTML) is the standard
markup language for creating
web pages and
web applications. With
Cascading Style Sheets (CSS) and
JavaScript, it forms a triad of
cornerstone technologies for the World Wide Web.
Web browsers receive HTML documents from a
web server or from local storage and
render the documents into multimedia web pages. HTML describes the structure of a web page
semantically and originally included cues for the appearance of the document.
HTML elements are the building blocks of HTML pages. With HTML constructs,
images and other objects such as
interactive forms may be embedded into the rendered page. HTML provides a means to create
structured documents by denoting structural
semantics for text such as headings, paragraphs, lists,
links, quotes, and other items. HTML elements are delineated by
tags, written using
angle brackets. Tags such as and directly introduce content into the page. Other tags, such as , surround and provide information about document text and may include other tags as sub-elements. Browsers do not display the HTML tags, but use them to interpret the content of the page. HTML can embed programs written in a
scripting language such as
JavaScript, which affects the behaviour and content of web pages. Inclusion of CSS defines the look and layout of content. The
World Wide Web Consortium (W3C), maintainer of both the HTML and the CSS standards, has encouraged the use of CSS over explicit presentational HTML
Linking Most web pages contain hyperlinks to other related pages and perhaps to downloadable files, source documents, definitions, and other web resources. In the underlying HTML, a hyperlink is coded like this: Example.org Homepage. s Such a collection of useful, related resources interconnected via hypertext links is dubbed a
web of information. Publication on the Internet created what Tim Berners-Lee first called the
WorldWideWeb (in its original
CamelCase, which was subsequently discarded) in November 1990. The hyperlink structure of the web is described by the
webgraph: the nodes of the web graph correspond to the web pages (or URLs), the directed edges between them to the hyperlinks. Over time, many web resources pointed to by hyperlinks disappear, relocate, or are replaced with different content. This makes hyperlinks obsolete, a phenomenon referred to in some circles as link rot, and the hyperlinks affected by it are often called
"dead" links. The ephemeral nature of the Web has prompted many efforts to archive websites. The
Internet Archive, active since 1996, is the best known of such efforts.
www prefix Many hostnames used for the World Wide Web begin with
www because of the long-standing practice of naming
Internet hosts according to the services they provide. The
hostname of a
web server is often
www, in the same way that it may be
ftp for an
FTP server, and
news or
nntp for a
Usenet news server. These hostnames appear as Domain Name System (DNS) or
subdomain names, as in
www.example.com. The use of
www is not required by any technical or policy standard and many websites do not use it; the first web server was
nxoc01.cern.ch. According to Paolo Palazzi, who worked at CERN along with Tim Berners-Lee, the popular use of
www as subdomain was accidental; the World Wide Web project page was intended to be published at www.cern.ch while info.cern.ch was intended to be the CERN home page; however the DNS records were never switched, and the practice of prepending
www to an institution's website domain name was subsequently copied. Many established websites still use the prefix, or they employ other subdomain names such as
www2,
secure or
en for special purposes. Many such web servers are set up so that both the main domain name (e.g., example.com) and the
www subdomain (e.g., www.example.com) refer to the same site; others require one form or the other, or they may map to different websites. The use of a subdomain name is useful for
load balancing incoming web traffic by creating a
CNAME record that points to a cluster of web servers. Since, currently, only a subdomain can be used in a CNAME, the same result cannot be achieved by using the bare domain root. When a user submits an incomplete domain name to a web browser in its address bar input field, some web browsers automatically try adding the prefix "www" to the beginning of it and possibly ".com", ".org" and ".net" at the end, depending on what might be missing. For example, entering "" may be transformed to
http://www.microsoft.com/ and "openoffice" to
http://www.openoffice.org. This feature started appearing in early versions of
Firefox, when it still had the working title 'Firebird' in early 2003, from an earlier practice in browsers such as
Lynx. It is reported that Microsoft was granted a US patent for the same idea in 2008, but only for mobile devices.
Scheme specifiers The scheme specifiers
http:// and
https:// at the start of a web
URI refer to
Hypertext Transfer Protocol or
HTTP Secure, respectively. They specify the communication protocol to use for the request and response. The HTTP protocol is fundamental to the operation of the World Wide Web, and the added encryption layer in HTTPS is essential when browsers send or retrieve confidential data, such as passwords or banking information. Web browsers usually automatically prepend http:// to user-entered URIs, if omitted.
Pages A
web page (also written as
webpage) is a document that is suitable for the World Wide Web and
web browsers. A web browser displays a web page on a
monitor or
mobile device. The term
web page usually refers to what is visible, but may also refer to the contents of the
computer file itself, which is usually a
text file containing
hypertext written in
HTML or a comparable
markup language. Typical web pages provide hypertext for browsing to other web pages via
hyperlinks, often referred to as
links. Web browsers will frequently have to access multiple
web resource elements, such as reading
style sheets,
scripts, and images, while presenting each web page. On a network, a web browser can retrieve a web page from a remote
web server. The web server may restrict access to a private network, such as a corporate intranet. The web browser uses the
Hypertext Transfer Protocol (HTTP) to make such requests to the web server. A
static web page is delivered exactly as stored, as
web content in the web server's
file system. In contrast, a
dynamic web page is generated by a
web application, usually driven by
server-side software. Dynamic web pages are used when each user may require completely different information, for example, bank websites, web email, etc.
Static page A
static web page (sometimes called a
flat page/stationary page) is a
web page that is delivered to the user exactly as stored, in contrast to
dynamic web pages which are generated by a
web application. Consequently, a static web page displays the same information for all users, from all contexts, subject to modern capabilities of a
web server to
negotiate content-type or language of the document where such versions are available and the server is configured to do so.
Dynamic pages and
MySQL)|frame A
server-side dynamic web page is a
web page whose construction is controlled by an
application server processing server-side scripts. In server-side scripting,
parameters determine how the assembly of every new web page proceeds, including the setting up of more client-side processing. A
client-side dynamic web page processes the web page using JavaScript running in the browser. JavaScript programs can interact with the document via
Document Object Model, or DOM, to query page state and alter it. The same client-side techniques can then dynamically update or change the DOM in the same way. A dynamic web page is then reloaded by the user or by a
computer program to change some variable content. The updated information could come from the server, or from changes made to that page's DOM. This may or may not truncate the browsing history or create a saved version to go back to, but a
dynamic web page update using
Ajax technologies will neither create a page to go back to nor truncate the
web browsing history forward of the displayed page. Using Ajax technologies, the end
user gets
one dynamic page managed as a single page in the
web browser while the actual
web content rendered on that page can vary. The Ajax engine sits only on the browser requesting parts of its DOM,
the DOM, for its client, from an application server. Dynamic HTML, or DHTML, is the umbrella term for technologies and methods used to create web pages that are not
static web pages, though it has fallen out of common use since the popularisation of
AJAX, a term which is now itself rarely used. Client-side scripting, server-side scripting, or a combination of these make for the dynamic web experience in a browser.
JavaScript is a
scripting language that was initially developed in 1995 by
Brendan Eich, then of
Netscape, for use within web pages. The standardised version is
ECMAScript.
Website website A
website is a collection of related web resources including
web pages,
multimedia content, typically identified with a common
domain name, and published on at least one
web server. Notable examples are
wikipedia.org,
google.com, and
amazon.com. A website may be accessible via a public
Internet Protocol (IP) network, such as the
Internet, or a private
local area network (LAN), by referencing a
uniform resource locator (URL) that identifies the site. Websites can have many functions and can be used in various fashions; a website can be a
personal website, a corporate website for a company, a government website, an organisation website, etc. Websites are typically dedicated to a particular topic or purpose, ranging from entertainment and
social networking to providing news and education. All publicly accessible websites collectively constitute the World Wide Web, while private websites, such as a company's website for its employees, are typically a part of an
intranet. Web pages, which are the building blocks of websites, are
documents, typically composed in
plain text interspersed with
formatting instructions of Hypertext Markup Language (
HTML,
XHTML). They may incorporate elements from other websites with suitable
markup anchors. Web pages are accessed and transported with the
Hypertext Transfer Protocol (HTTP), which may optionally employ encryption (
HTTP Secure, HTTPS) to provide security and privacy for the user. The user's application, often a
web browser, renders the page content according to its HTML markup instructions onto a
display terminal.
Hyperlinking between web pages conveys to the reader the
site structure and guides the navigation of the site, which often starts with a
home page containing a directory of the site
web content. Some websites require user registration or
subscription to access content. Examples of
subscription websites include many business sites, news websites,
academic journal websites, gaming websites, file-sharing websites,
message boards, web-based
email,
social networking websites, websites providing real-time price quotations for different types of markets, as well as sites providing various other services.
End users can access websites on a range of devices, including
desktop and
laptop computers,
tablet computers,
smartphones, and
smart TVs.
Browser A
web browser (commonly referred to as a
browser) is a
software user agent for accessing information on the World Wide Web. To connect to a website's
server and display its pages, a user needs to have a web browser program. This is the program that the user runs to download, format, and display a web page on the user's computer. In addition to allowing users to find, display, and move between web pages, a web browser will usually have features like keeping bookmarks, recording history, managing cookies (see below), and home pages and may have facilities for recording passwords for logging into websites. The most popular browsers are
Chrome,
Safari,
Edge,
Samsung Internet and
Firefox.
Server web server, a computer designed for
rack mounting A
Web server is
server software, or hardware dedicated to running said software, that can satisfy World Wide Web client requests. A web server can, in general, contain one or more websites. A web server processes incoming network requests over
HTTP and several other related protocols. The primary function of a web server is to store, process and deliver
web pages to
clients. The communication between client and server takes place using the
Hypertext Transfer Protocol (HTTP). Pages delivered are most frequently
HTML documents, which may include
images,
style sheets and
scripts in addition to the text content. servers are installed together to be used for the
Wikimedia Foundation. A
user agent, commonly a
web browser or
web crawler, initiates communication by making a
request for a specific resource using HTTP and the server responds with the content of that resource or an
error message if unable to do so. The resource is typically a real file on the server's
secondary storage, but this is not necessarily the case and depends on how the web server is
implemented. While the primary function is to serve content, full implementation of HTTP also includes ways of receiving content from clients. This feature is used for submitting
web forms, including
uploading of files. Many generic web servers also support
scripting using
Active Server Pages (ASP),
PHP (Hypertext Preprocessor), or other
scripting languages. This means that the behaviour of the web server can be scripted in separate files, while the actual server software remains unchanged. Usually, this function is used to generate HTML documents
dynamically ("on-the-fly") as opposed to returning
static documents. The former is primarily used for retrieving or modifying information from
databases. The latter is typically much faster and more easily
cached but cannot deliver
dynamic content. Web servers can also frequently be found
embedded in devices such as
printers,
routers,
webcams and serving only a
local network. The web server may then be used as a part of a system for monitoring or administering the device in question. This usually means that no additional software has to be installed on the client computer since only a web browser is required (which now is included with most
operating systems).
Optical networking Optical networking is a sophisticated infrastructure that utilises optical fibre to transmit data over long distances, connecting countries, cities, and even private residences. The technology uses optical microsystems like
tunable lasers, filters,
attenuators, switches, and wavelength-selective switches to manage and operate these networks. The large quantity of optical fibre installed throughout the world at the end of the twentieth century set the foundation of the Internet as it is used today. The information highway relies heavily on optical networking, a method of sending messages encoded in light to relay information in various telecommunication networks. The
Advanced Research Projects Agency Network (ARPANET) was one of the first iterations of the Internet, created in collaboration with universities and researchers in 1969. However, access to the ARPANET was limited to researchers, and in 1985, the
National Science Foundation founded the
National Science Foundation Network (NSFNET), a program that provided supercomputer access to researchers. The privatisation of the Internet and the release of the World Wide Web to the public in 1993 led to an increased demand for Internet capabilities. This spurred developers to seek solutions to reduce the time and cost of laying new fibre and increase the amount of information that can be sent on a single fibre, to meet the growing needs of the public. In 1994, Pirelli S.p.A.'s optical components division introduced a wavelength-division multiplexing (WDM) system to meet growing demand for increased data transmission. This four-channel WDM technology allowed more information to be sent simultaneously over a single optical fibre, effectively boosting network capacity. Pirelli wasn't the only company that developed a WDM system; another company, the
Ciena Corporation (Ciena), created its own technology to transmit data more efficiently.
David Huber, an optical networking engineer and entrepreneur
Kevin Kimberlin founded Ciena in 1992. Drawing on laser technology from
Gordon Gould and William Culver of
Optelecom, Inc., the company focused on utilising optical amplifiers to transmit data via light. Under chief executive officer Pat Nettles, Ciena developed a dual-stage optical amplifier for dense wavelength-division multiplexing (DWDM), patented in 1997 and deployed on the Sprint network in 1996.
Cookie An
HTTP cookie (also called
web cookie,
Internet cookie,
browser cookie, or simply
cookie) is a small piece of data sent from a website and stored on the user's computer by the user's
web browser while the user is browsing. Cookies were designed to be a reliable mechanism for websites to remember
stateful information (such as items added in the shopping cart in an online store) or to record the user's browsing activity (including clicking particular buttons,
logging in, or recording which pages were visited in the past). They can also be used to remember arbitrary pieces of information that the user previously entered into form fields, such as names, addresses, passwords, and credit card numbers. Cookies perform essential functions in the modern web. Perhaps most importantly,
authentication cookies are the most common method used by web servers to know whether the user is logged in or not, and which account they are logged in with. Without such a mechanism, the site would not know whether to send a page containing sensitive information or require the user to authenticate themselves by logging in. The security of an authentication cookie generally depends on the security of the issuing website and the user's
web browser, and on whether the cookie data is encrypted. Security vulnerabilities may allow a cookie's data to be read by a
hacker, used to gain access to user data, or used to gain access (with the user's credentials) to the website to which the cookie belongs (see
cross-site scripting and
cross-site request forgery for examples). Tracking cookies, and especially third-party tracking cookies, are commonly used as ways to compile long-term records of individuals' browsing histories a potential
privacy concern that prompted European and U.S. lawmakers to take action in 2011. European law requires that all websites targeting
European Union member states gain "informed consent" from users before storing non-essential cookies on their device. Google
Project Zero researcher Jann Horn describes ways cookies can be read by
intermediaries, like
Wi-Fi hotspot providers. When in such circumstances, he recommends using the browser in
private browsing mode (widely known as
Incognito mode in Google Chrome).
Search engine engine A
web search engine or
Internet search engine is a
software system that is designed to carry out
web search (
Internet search), which means to search the World Wide Web in a systematic way for particular information specified in a
web search query. The search results are generally presented in a line of results, often referred to as
search engine results pages (SERPs). The information may be a mix of
web pages, images, videos, infographics, articles, research papers, and other types of files. Some search engines also
mine data available in
databases or
open directories. Unlike
web directories, which are maintained only by human editors, search engines also maintain
real-time information by running an
algorithm on a
web crawler. Internet content that is not capable of being searched by a web search engine is generally described as the
deep web. In 1990,
Archie, the world's first search engine, was released. The technology was originally an index of
File Transfer Protocol (FTP) sites, which was a method for moving files between a client and a server network. This early search tool was superseded by more advanced engines like
Yahoo! in 1995 and
Google in 1998.
Deep web The deep web,
invisible web, or
hidden web are parts of the World Wide Web whose contents are not
indexed by standard
web search engines. The opposite term to the deep web is the
surface web, which is accessible to anyone using the Internet.
Computer scientist Michael K. Bergman is credited with coining the term
deep web in 2001 as a search indexing term. and includes many very common uses such as
web mail,
online banking, and services that users must pay for, and which is protected by a
paywall, such as
video on demand, some online magazines and newspapers, among others. The content of the deep web can be located and accessed by a direct
URL or
IP address and may require a password or other security access past the public website page.
Caching A
web cache is a server computer located either on the public Internet or within an enterprise that stores recently accessed web pages to improve response time for users when the same content is requested within a certain time after the original request. Most web browsers also implement a
browser cache by writing recently obtained data to a local data storage device. HTTP requests by a browser may ask only for data that has changed since the last access. Web pages and resources may contain expiration information to control caching to secure sensitive data, such as in
online banking, or to facilitate frequently updated sites, such as news media. Even sites with highly dynamic content may permit basic resources to be refreshed only occasionally. Website designers find it worthwhile to collate resources such as CSS data and JavaScript into a few site-wide files so that they can be cached efficiently. Enterprise
firewalls often cache Web resources requested by one user for the benefit of many users. Some
search engines store cached content of frequently accessed websites. == Security ==