Carillon and programmable logic controller: what they have in common

1. Step 1. Carillon — has part — Pinned cylinder. Automatic carillons have a pinned drum.
2. Step 2. Pinned cylinder — works like — Punched card. Pins on a cylinder and holes in a card are two ways of recording a sequence for a machine.
3. Step 3. Punched card — is used in — Harvard Mark I. The program was read from punched tape and the data from punched cards.
4. Step 4. Harvard Mark I — has part — Relay. The Mark I was electromechanical, built from relays.
5. Step 5. Relay — evolved into — Programmable logic controller. It replaced relay cabinets.

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