{{Infobox
| title = Internet
| image = https://commons.wikimedia.org/wiki/Special:FilePath/Internet%20map%201024.jpg?width=320
| caption = A network of networks: no centre, many paths
| label1 = Type
| data1 = Global packet-switched network
| label2 = Predecessor
| data2 = ARPANET (1969)
| label3 = Core protocols
| data3 = TCP/IP, adopted 1 January 1983
| label4 = Governance
| data4 = Distributed; no central authority
}}

The '''Internet''' is a global system of interconnected computer networks that communicate using a shared set of protocols. It is not a network but a network of networks: independently owned and operated systems that agree only on how to pass data between one another. The [[World Wide Web]], email and streaming media are applications that run on it, not the thing itself.

== Design principles ==

Three decisions account for most of what the Internet is and is not.

; Packet switching : Data is divided into packets, each carrying a destination address and travelling independently. Routers forward each packet towards its destination one hop at a time. No circuit is reserved in advance, so a link is shared by every conversation crossing it, and traffic can route around a failure without any central controller noticing.
; The end-to-end principle : The network's job is to move packets. Reliability, ordering, encryption and everything else belong at the endpoints. A network that promises little is one that a new application can use without asking permission. The Web, voice calls and video were all deployed without changing the network itself.
; Layering : Protocols are stacked. IP moves packets between hosts; TCP adds reliable ordered delivery on top; applications sit above that. Each layer can be replaced without disturbing the others, which is how the transition from IPv4 to IPv6 can proceed without rewriting applications.

== History ==

Packet switching was proposed independently by Paul Baran in the United States and Donald Davies in the United Kingdom in the early 1960s. ARPANET, funded by the US Advanced Research Projects Agency, connected its first four nodes in 1969.

The problem that produced the Internet proper was joining ARPANET to other, differently designed networks. Vinton Cerf and Robert Kahn's 1974 design for TCP handled this by asking the networks in between to do as little as possible.<ref>Cerf, V. and Kahn, R. "A Protocol for Packet Network Intercommunication". ''IEEE Transactions on Communications'', 1974.</ref> ARPANET switched to TCP/IP on 1 January 1983, the date usually given as the Internet's birth.

The Domain Name System arrived in 1983, replacing a single manually distributed file of host names. The National Science Foundation's NSFNET became the backbone through the 1980s, carrying a policy restricting it to research use; commercial restrictions were lifted in the early 1990s, and the network opened to the public. [[World Wide Web|The Web]] followed, and with it the Internet's move from a specialists' tool to general infrastructure.

== Structure ==

The Internet has no centre and no owner. It consists of tens of thousands of independent networks, called autonomous systems, that exchange traffic under bilateral agreements: peering, where two networks swap traffic at no charge, and transit, where one pays another for onward delivery. The Border Gateway Protocol propagates the routes between them.

Certain coordination functions must be global, because names and numbers have to be unique. Addresses and domain names are allocated through the Internet Assigned Numbers Authority and the regional registries, and protocol standards are published as Requests for Comments by the Internet Engineering Task Force, an open body that works by rough consensus and running code.

== Applications ==

{| class="wikitable"
! Application !! Protocol !! Introduced
|-
| Email || SMTP || 1971 (ARPANET), standardised 1982
|-
| File transfer || FTP || 1971
|-
| Domain names || DNS || 1983
|-
| The Web || HTTP || 1991
|-
| Real-time media || RTP and successors || 1996
|}

== Social effects ==

The Internet lowered the cost of distributing information to near zero, which redistributed influence away from those who previously owned the means of distribution (publishers, broadcasters, record labels) and towards platforms that aggregate attention. The same property that lets a dissident publish without a printing press lets a fraud reach millions. Debates over moderation, surveillance, network neutrality and the concentration of platform power are all, at bottom, arguments about who gets to decide what a permissionless network carries.

== See also ==

* [[World Wide Web]]
* [[Computer]]
* [[Hypertext]]
* [[Free software]]

== References ==

<references />

[[Category:Computing]]
[[Category:Technology]]