How a relay made a computer decision
A relay is an electrically controlled switch. When current passes through its coil, the coil becomes an electromagnet and pulls a small metal armature, opening or closing contacts in another circuit. In a computer, those two conditions could stand for the binary values 0 and 1.
Linked relays could do more than store a single bit. Their contacts routed electrical signals through logic circuits: combinations of on and off states could add numbers, compare values, or decide which operation should happen next. A program’s instructions determined how those circuits were used, turning banks of physical switches into a machine that could carry out a sequence of calculations.
The cost of moving metal
Relays offered a practical route to automatic computation before compact electronic switches were available. But every change of state required a physical part to move. That made switching slow compared with later electronic computers, and moving contacts could wear, stick, or need adjustment. Large machines also demanded careful wiring: one faulty connection could disrupt a chain of operations.
The audible clicks were a by-product of computation, not a signal that a person had to interpret. As vacuum tubes and then transistors took over switching, computers could change states without moving an armature each time. The change was more than a quieter room: it made faster, denser circuits possible, so a calculation that once depended on thousands of coordinated mechanical movements could eventually happen in solid-state electronics.
