Party-Line Computers

For all their forbidding, mechanical bulk, the intricate electronic computers that control so much of U.S. science and industry are often sociable contraptions. Like the human beings who built them, they occasionally succumb to a compulsive need for communication with others of their own kind. Faced with a problem that seems too tough to solve, one computer is perfectly capable of seeking help from another.

Unable to complete its assigned task, a small, provincial computer may send an electronic S O S to a big brother in an other city -- provided it has already been connected to its collaborator by coaxial cable and microwave radio. Computers now being set up to keep track of seat reservations for U.S. airlines will have to chatter with one another day and night.

Lest the nation's growing army of me chanical brains eventually crowd the U.S.

housewife off her familiar telephone cir cuits and run up far too big a bill of their own, scientists for International Business Machines are already developing a private computer-communications system.

Computer talk can be fed easily into the country's microwave relay system, the high, hilltop relay stations that are a familiar part of the U.S. landscape. But IBM engineers decided not to get into ex pensive competition with the radio and TV programs, the phone calls, and all the other electronic chitchat, which now jump in short line-of-sight hops from coast to coast. Instead, the computer men are mak ing use of a basic but seldom used proper ty of microwaves.

Remembering that radio waves diffract (bend) around obstructions, the IBM engineers calculated that they could twist their transmissions right over the top of mountains and other obstructions with out building repeater stations on top. They set up a weak, 15-watt transmitter 45 miles south of San Jose, Calif., on the other side of Loma Prieta, a 3,798-ft. peak in the Santa Cruz mountains. Then they pointed their transmitter's beam of 1,855-megacycle waves in the general direction of San Jose. When the beam was aimed too high, its waves shot off into space; when the beam was too low, its waves were lost in the mountainside. But when the beam was angled just right, its waves hit the upper edge of the mountain and a small part of the radio energy was diffracted down to a sensitive receiving set in San Jose.

IBM feels sure that a microwave system using bare and costless ridges of land instead of expensive repeater stations could carry computer chatter all over the country. It would probably be too noisy to carry human conversation, but unlike their creators, computers are not bothered by noise on the phone line.

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