As we’ve seen, tubes were extremely delicate and difficult to make; they required a lot of electricity and gave off great heat. Switches—the mechanisms by which each customer’s call was passed along the system’s vast grid to the precise party he was calling—were prone to similar problems. They were delicate mechanical devices; they used relays that employed numerous metal contacts; they could easily stop working and would eventually wear out. They were also, because they clicked open and closed, far slower than an electronic switch, without moving parts, might be.
