digitalis

In Latin, digitus meant finger or toe. Farmers counted on digits. Merchants calculated on digits. The word was the body part and the unit of counting — they were the same thing. When medieval scholars and merchants needed words for their systems of reckoning, they borrowed from what was already there. Arithmetic moved from fingers to the abacus to written numerals, but the connection to digits never quite disappeared from the vocabulary.

The technological leap came in the 1900s. In 1931, Alec Reeves at the Siemens Laboratories in London began experimenting with pulse code modulation — the idea that you could transmit information as a series of pulses, as opposed to continuous wave signals. Each pulse was either on or off. Like a finger pointing or not pointing. The term 'digital' appeared in academic papers around 1938, referring to the discrete-step nature of the information — step by step, digit by digit, one or zero.

The IBM Mark I, built in 1944, was one of the first computers called 'digital' to distinguish it from 'analog' machines, which worked with continuous physical quantities. The vocabulary was already layered: digit meant finger, then it meant numeral, then it meant a discrete unit of information. The Latin word that meant 'pointing thing' was being used to describe machines that were essentially counting in binary, the simplest finger mathematics possible.

By the 1960s, 'digital' had become the dominant metaphor for computers that worked with discrete on-off switches rather than sliding scales. The transistor, the microchip, the bit — all of them descended from the medieval word for a unit you could count on your fingers. We kept using the finger metaphor long after we stopped using our fingers. The oldest tool still names the newest one.