A wonderful educational film (made by British Telecommunications) showing how telephone exchanges work and how they connect one telephone to another when you make a call. From the earliest mechanical switches to the latest (well in 1982 anyway) microchip technology. The film does a good job at explaining the basics at how these systems work and why they are needed.
It reminds me when my Dad took me to his work at a telephone exchange in the late 1970s, big rooms full of switches and wires. It's probably all replaced by a single box on the wall now.
