COMPUTER MEMORIES, Chapter 50

AIRLINE COMMUNICATIONS
One time we installed two RCA 4102 computers in an airline communication center. As you may imagine, those computers must run at all times, even when the electric power goes out. Often they use batteries or generators for back-up, but here they had a 15 or 20 foot flywheel that was kept spinning by a small electric motor. When power went off, the flywheel kept spinning and kept a generator running for 15 to 20 minutes or so, long enough to get other back-up power supplies up and running.

This was called a “store and forward” communication system. That is, receive the message, store it until a line is available, then forward the message to its destination. If you drew a map of the US, showing all the cities where an airplane might land, then connect each of them to each of the others, you would have a map just covered with lines. With this store and forward computer system, just one line was needed, connecting each city to Chicago where the computer was installed. Then everyone in all those cities sent all of their messages to the computer in Chicago. That computer would receive them, store them, then send them wherever they needed to go, when a line became available.

It’s a little different in application, but the way Fed-Ex distributes packages, and the “hub and spoke” airline systems, use this same philosophy. For example, to send a package from Los Angeles to Phoenix, it would be loaded on an airplane in Los Angeles, flown to Nashville, Tenn., then sorted and placed on a plane returning to Phoenix, and on and on. Use your imagination! The airplane from Los Angeles would contain packages from Southern California, going to a thousand destinations, then the packages would be sorted and placed on airplanes that had arrived in Nashville from hundreds of airports, and the planes would then return to the city where it originated, loaded with the packages from a thousand other locations.