In the earliest days of electronic computers, each computer stood completely alone. Each new machine represented a unique design, with its own architecture, operating codes, and methods of storing data. The early computer engineers were staggeringly ingenious in coming up with different ways of representing binary information. On different machines, ones and zeroes were represented by switching vacuum tubes, or magnetized patches on rotating metal drums, or bright and dark spots on oscilloscope screens – even by patterns of sound waves travelling through tubes filled with mercury. But two storage methods quickly became standard, allowing data to be shared between machines: IBM punch cards and magnetic tapes. If you have ever seen a computer in an old movie from the 1960s, you probably saw the whirring tape machines and clattering card punches in among the huge banks of machinery with their innumerable blinking lights.

The trouble with punch cards and magnetic tapes is that they have to be physically carried from one computer to another, and that is a slow process. By the end of the fifties, the U.S. military was using dedicated telephone lines to link computers together electronically. The SAGE network, as it was called, allowed several large computers to quickly share incoming data from the radar stations that continuously scanned the skies in case of a Russian nuclear attack. This worked because all the computers in the SAGE network were identical, so there was no trouble about translation. Other early networks had the same limitation. They either connected similar mainframe computers together, or connected one computer to many identical terminals. There was no general way of connecting different computers on the same network.

[Read more…]