All this began in an obscure branch of the U.S. Department of Defense called the Advanced Research Projects Agency, or ARPA. In the 1960s a number of computer scientists at universities and research laboratories across the country received ARPA funding for projects that might have defense-related potential—anything from graphics to artificial intelligence. With the researchers' needs for processing power steadily growing, ARPA decided to join its scattered mainframes into a kind of cooperative, allowing the various groups to draw on one another's computational resources. Responsibility for creating the network was assigned to Lawrence Roberts, a young computer scientist who arrived at ARPA from the Massachusetts Institute of Technology in 1966. All this began in an obscure branch of the U.S. Department of Defense called the Advanced Research Projects Agency, or ARPA. In the 1960s a number of computer scientists at universities and research laboratories across the country received ARPA funding for projects that might have defense-related potential—anything from graphics to artificial intelligence. With the researchers' needs for processing power steadily growing, ARPA decided to join its scattered mainframes into a kind of cooperative, allowing the various groups to draw on one another's computational resources. Responsibility for creating the network was assigned to Lawrence Roberts, a young computer scientist who arrived at ARPA from the Massachusetts Institute of Technology in 1966. Roberts was aware of a promising approach in the ideas of an MIT classmate, Leonard Kleinrock, and he later learned of related work by two other communications experts, Paul Baran and Donald Davies. - Kleinrock had written his doctoral dissertation on the flow of messages in communications networks, exploring the complexities of moving data in small chunks. At about the same time, Baran proposed a different kind of telephone network, which would turn the analog signal of a telephone into digital bits, divide the stream into blocks, and send the blocks in several different directions across a network of high-speed switches or nodes; the node nearest the destination would put the pieces back together again. Davies proposed a similar scheme, in which he called the chunks or blocks "packets," as in packet switching, and that name stuck.
- Roberts, for his part, was convinced that the telephone system's method of routing signals, called circuit switching, was poorly suited for linking computers: to connect two callers, a telephone switch opens a circuit, leaving it open until the call is finished. Computers, however, often deliver data in bursts and thus don't need full-time possession of a connection. Packet switching seemed the obvious choice for ARPA's network, not only enabling several computers to share a circuit but also countering congestion problems: when one path was in heavy use, a packet could simply take another route.
Initially, Roberts intended to have the switching done by the mainframes that ARPA wanted to connect. But small, speedy minicomputers were just then appearing, and an adviser, Wesley Clark of Washington University in St. Louis, persuaded him to assign one of them to each of the research centers as a switch. Unlike the mainframes, which came from a variety of manufacturers, these so-called interface message processors, or IMPs, could have standardized routing software, which would save on programming costs and allow easy upgrades. In early 1969 the job of building and operating the network was awarded to the consulting firm of Bolt Beranek and Newman, Inc. (BBN), in Cambridge, Massachusetts. Although modest in size, BBN employed a stellar cast of engineers and scientists, drawn largely from nearby Harvard University and MIT. Initially, Roberts intended to have the switching done by the mainframes that ARPA wanted to connect. But small, speedy minicomputers were just then appearing, and an adviser, Wesley Clark of Washington University in St. Louis, persuaded him to assign one of them to each of the research centers as a switch. Unlike the mainframes, which came from a variety of manufacturers, these so-called interface message processors, or IMPs, could have standardized routing software, which would save on programming costs and allow easy upgrades. In early 1969 the job of building and operating the network was awarded to the consulting firm of Bolt Beranek and Newman, Inc. (BBN), in Cambridge, Massachusetts. Although modest in size, BBN employed a stellar cast of engineers and scientists, drawn largely from nearby Harvard University and MIT. Roberts had outlined what the IMPs would do. First, they would break data from a host mainframe into packets of about 1,000 bits each, attaching source and destination information to each packet, along with digits used to check for transmission errors. The IMPs would then choose optimal routes for the individual packets and reassemble the message at the other end. All the traffic would flow on leased telephone lines that could handle 50,000 bits per second. The BBN team, led by Robert Kahn of MIT, worked out the details and devised an implementation strategy. ARPANET was up and running at four sites by late 1969. At first, just four time-sharing computers were connected, but more hosts and nodes quickly followed, and the network was further expanded by reconfiguring the IMPs so they could accept data from small terminals as well as mainframes. The nature of the traffic was not what ARPA had expected, however. As time went on, the computer scientists on the network used it primarily for personal communication rather than resource sharing. The first program for sending electronic mail from one computer to another was written in 1972—almost on a whim—by Ray Tomlinson, an engineer at BBN. He earned a kind of alphanumerical immortality in the process. For his addressing format he needed a symbol to clearly separate names from computer locations. He looked at the keyboard in front of him and made a swift choice: "The one that was most obvious was the @ sign, because this person was @ this other computer," he later explained. "At the time, there was nobody with an @ sign in their name that I was aware of." Trillions of e-mails would be stamped accordingly.
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