“The PLL was one of the great innovations of electronics”
I’m barely a hardware guy, mostly curious and lightweight reading.
It’s interesting to think about the clever, small, electrical and mechanical mechanisms that have been invented.
Getting back to the rotary phones. How in the world could the exchanges take those pulses and connect thousands of callers to their destinations all at once with bunches of relays?
The electromechanical steampunk complexity of the Strowger switch is such that it's hard to believe that hundreds of millions of them were made to work together in the Bell System, such a vital catalyst to the rise of American civilization throughout most of the 20th century.
Your phone — the dial phone that sat somewhere in your house, or your parent's house — connected to the phone network by a wire, was matched by a rack bay at the "Central Office" of the phone company. Each and every phone had about ten inches of 19" rack space devoted to it; the rent you paid for the phone also paid for that rack space, and the Strowger switches and other wiring that occupied it, as well as (of course) the power supply necessary to make it run when you picked up the receiver and released the switch hook, connecting the phone to the system.
There are a number of YouTube videos on this — and many related — subjects.
A very carefully crafted network of switches and trunks. Off-hook activates a "line finder" in a Strowger switch. As the first number is dialed, the switch armature ratchets upward, then rotates to another Strowger switch to the next number. On the 3rd number, the switch finds a "trunk" to another exchange. A line finder on that exchange goes through a set of 4 Strowger switches to land on the terminating subscriber line. For "long distance", the +1 jumps right on a switch very high in the hierarchy and steps down to the destination. Next generation switches were "crossbar" with "fine motion" versus the large motions of the Strowger switch. Finer crossbar switches were employed at "toll" offices to make "long distance" call. The limiting factor for this kind of telephone network is the need to have a fully dedicated wire path end to end. In the digital age we can queue/buffer information, speed up transmission rates and leverage switch fabrics with very high capacity in a smaller physical space.