# ARPANET ARPANET (Advanced Research Projects Agency Network) was the first wide-area packet-switching network and the direct predecessor to the modern [[Internet]]. Funded by [[DARPA]] (then called ARPA), the network went live on October 29, 1969, when the first message was sent from UCLA to Stanford Research Institute—the system crashed after transmitting just "LO" (attempting "LOGIN"). The project emerged from [[J.C.R. Licklider]]'s vision of an "Intergalactic Computer Network" and was developed under the leadership of [[Bob Taylor]] and [[Larry Roberts]]. ARPANET introduced several foundational concepts: [[Packet Switching]] (breaking data into packets routed independently), distributed architecture (no central point of failure), and later [[TCP/IP]] (developed by [[Vint Cerf]] and [[Bob Kahn]]). By 1971, it connected 15 nodes including MIT, Harvard, and BBN. The network enabled email (1971), file transfer, and remote login—proving that heterogeneous computers could communicate. ARPANET was decommissioned in 1990, having evolved into the Internet. Contrary to myth, it wasn't designed primarily for nuclear attack survival—that was a beneficial side effect of its distributed design. ## ARPANET Evolution ``` ┌─────────────────────────────────────────────────────────────┐ │ ARPANET TIMELINE │ ├─────────────────────────────────────────────────────────────┤ │ │ │ 1962 Licklider's "Intergalactic Network" vision │ │ │ │ │ ▼ │ │ 1966 Bob Taylor secures funding │ │ │ │ │ ▼ │ │ 1969 First ARPANET nodes (4 sites) │ │ │ UCLA ──── SRI ──── UCSB ──── Utah │ │ │ │ │ ▼ │ │ 1971 15 nodes, email invented (Ray Tomlinson) │ │ │ │ │ ▼ │ │ 1973 First international connections (UK, Norway) │ │ │ │ │ ▼ │ │ 1974 TCP/IP proposed (Cerf & Kahn) │ │ │ │ │ ▼ │ │ 1983 ARPANET switches to TCP/IP ("Flag Day") │ │ │ MILNET splits off for military use │ │ │ │ │ ▼ │ │ 1990 ARPANET decommissioned │ │ │ │ │ ▼ │ │ 1991+ Internet + World Wide Web era │ │ │ └─────────────────────────────────────────────────────────────┘ ``` ## Key Innovations | Innovation | Description | Impact | |------------|-------------|--------| | **[[Packet Switching]]** | Data split into packets, routed independently | Efficient, resilient data transmission | | **Distributed architecture** | No central hub | No single point of failure | | **IMP (Interface Message Processor)** | Early router | Standardized network connection | | **NCP (Network Control Protocol)** | First host-to-host protocol | Enabled inter-computer communication | | **[[TCP/IP]]** | Transmission Control/Internet Protocol | Universal network language | | **Email** | Electronic messaging | Killer app of early network | ## Original Four Nodes (1969) | Node | Institution | IMP # | Role | |------|-------------|-------|------| | **UCLA** | University of California, Los Angeles | 1 | Network Measurement Center | | **SRI** | Stanford Research Institute | 2 | NIC (Network Information Center) | | **UCSB** | UC Santa Barbara | 3 | Culler-Fried Interactive Mathematics | | **Utah** | University of Utah | 4 | Graphics research | ## Key Figures | Person | Contribution | |--------|--------------| | [[J.C.R. Licklider]] | Vision of networked computing ("Lick") | | [[Bob Taylor]] | Secured ARPA funding, managed project | | [[Larry Roberts]] | Chief architect, program manager | | [[Vint Cerf]] | Co-inventor of TCP/IP | | [[Bob Kahn]] | Co-inventor of TCP/IP | | Leonard Kleinrock | Packet switching theory, UCLA node | | Ray Tomlinson | Invented email, @ symbol | | [[Douglas Engelbart]] | SRI node, invented mouse, hypertext demo | ## ARPANET vs Internet Myths | Myth | Reality | |------|---------| | "Built to survive nuclear war" | Distributed design helped, but not primary goal | | "Military network" | Research network for universities | | "Invented email" | Email emerged from ARPANET but wasn't the purpose | | "Became the Internet" | Evolved into Internet via TCP/IP adoption | ## Technical Architecture | Component | Function | |-----------|----------| | **Host** | User's computer | | **IMP** | Packet switch (router precursor) | | **TIP** | Terminal IMP (for dumb terminals) | | **NCP** | Original protocol (replaced by TCP/IP) | | **FTP** | File transfer | | **Telnet** | Remote terminal access | ## Growth Timeline | Year | Nodes | Milestone | |------|-------|-----------| | 1969 | 4 | First message sent | | 1971 | 15 | Email invented | | 1973 | 40 | International connections | | 1977 | 111 | Continued expansion | | 1983 | — | TCP/IP switchover | | 1990 | — | Decommissioned | ## Legacy | Legacy | Description | |--------|-------------| | **Internet** | Direct descendant via TCP/IP | | **Email** | First killer app, still dominant | | **Distributed systems** | Model for resilient networks | | **Open protocols** | Standards-based interoperability | | **Research collaboration** | Remote resource sharing | ## References - Abbate, Janet. *Inventing the Internet* (1999) - Hafner, Katie & Lyon, Matthew. *Where Wizards Stay Up Late* (1996) - https://en.wikipedia.org/wiki/ARPANET ## Related - [[DARPA]] - [[Internet]] - [[TCP/IP]] - [[Packet Switching]] - [[J.C.R. Licklider]] - [[Vint Cerf]] - [[Bob Kahn]] - [[Douglas Engelbart]] - [[World Wide Web]] - [[Tim Berners-Lee]] - [[Computing History]]