One of the main successes of ARPANET was the use of packet switching as a way of sending data from one computer to another.

Long distance networks used the existing telephone system infrastructure to connect computers to each other, but the circuit switching system used to place phone calls did not work well with computer data because data could be lost too easily.

Packet switching works by breaking a message up into small packages—or packets—each of which is delivered independently to the destination computer and reassembled when all packets have been received.

In essence, packet switching is equivalent to breaking up a very large shipment into multiple smaller packages. If a single package is lost in transmission, the receiving computer can request that the packet be resent from the source computer, which is faster than having to resend the entire shipment. In addition, because each packet travels independently over the network, they can be routed around slower connections, making the data transmission faster than it would be with a larger, single package.