Editing ARPANET (section)

=== Prehistory ===
'''Packet switching''' was developed by '''Paul Baran''' in the early 1960s under a '''RAND Corporation''' research project aimed at creating a communications network capable of surviving nuclear war. In Baran's own words:<blockquote>If the strategic weapons command and control systems could be more survivable, then the country’s retaliatory capability could better allow it to withstand an attack and still function; a more stable position. But this was not a wholly feasible concept, because long-distance communications networks at that time were extremely vulnerable and not able to survive attack. That was the issue.<ref>Abbate, J. 2000. _Inventing the Internet_. Inside Technology. MIT Press.  p.10</ref></blockquote>The problem is that conventional long-distance communications networks, such as the telephone network, operated in hierarchal and concentrated fashion. Calls are directed to a local, and, if necessary, a regional office, where they are routed manually. With each customer connected to only a single office, eliminating a single office would cut off a large number of nodes.<ref>Abbate, J. 2000. _Inventing the Internet_. Inside Technology. MIT Press. p.11</ref> So long as routing capabilities were centralized in offices, networks remained vulnerable. The Department of Defense, well aware of this, had already experimented with '''AUTOVON''', designed and operated by the American Telephone and Telegraph Company (AT&T) between 1961 and 1963. AUTOVON did not represent a technological advance. It was a military voice network built atop the existing civilian telephone network. A sort of decentralization was achieved by increasing the frequency of switching centers; overall survivability was increased by fortifying them. By automating the routing process and distributing this capability to every node in the network, Baran's system eliminated the need for switch centers altogether. “The intelligence required to switch signals to surviving links is at the link nodes and not at one or a few centralized switching centers."<ref>Abbate, J. 2000. _Inventing the Internet_. Inside Technology. MIT Press. p.16 (quoting Paul Baran)</ref>

Packet switching made decentralized computer-routing possible by creating a system in which an address was attached to the communique itself, allowing each node to automatically and independently route any data they received. Packets consist of header and payload. Data in the header directs the payload to its destination, where the payload is processed by a separate operating system. Data flow is now a function of properties immanent to the message itself without the transcendental intervention of any operator outside the system. ARPANET is the real body without organs. Moreover, packet switching vastly improved the efficiency of communication systems.

Essential to early computing is the development of '''time-sharing'''. Issuing commands to primitive computers was a laborious process involving punch cards and frequent disappointment. Countless hours spent punching holes in cards and fiddling with magnetic tape- and all the while the computers sit idle.<blockquote>Instead of running a single program from start to finish before going on to the next one, a time-sharing operating system would cycle between a number of programs, devoting a fraction of a second of processing time to each one before going on the next ... When a computer serves a user at a interactive terminal, it spends most of its time waiting for commands; very little time is spent actually processing data. If a computer can serve many terminals at once, it will spend less time idle and more time doing productive work, which increases the efficiency therefore the economically feasibility—of interactive computing.<ref>Abbate, J. 2000. _Inventing the Internet_. Inside Technology. MIT Press. p.24</ref></blockquote>By the mid 1960s, researchers regularly had access to time-sharing computers, and began to wonder if the principle behind time-sharing (high-speed cycling to simulate simultaneity) could be applied to communication between computers. Network communication suffered a temporal diseconomy similar to that of batch coding. Because computer messages typically came in short bursts separated by long pauses, computer users paid dearly for telephone connections that were inactive much of the time. Baran's packets- because they could be broken down into fractions, scattered, and reassembled independently- made possible the cycling operation necessary to efficiently distribute bandwidth.