Which unit of information did Shannon's 1948 theory of communication establish?

The bit - a name Shannon credited to a colleague, John Tukey, as a contraction of binary digit. His paper defined information as resolved uncertainty: a message is informative in proportion to how many possibilities it eliminates, so the content of a signal has nothing to do with its meaning.

That deliberate refusal to care about meaning is what made the theory general. It applies identically to a telegraph, a conversation, a photograph and a gene, and it produces hard limits - the channel capacity theorem says every noisy channel has a maximum error-free rate, and that codes exist to approach it. Every modem, hard drive, deep-space probe and phone call is engineered against that ceiling.

He was also unusually playful for someone who founded a field. He built a mechanical mouse that learned a maze, a machine whose only function was to switch itself off, a juggling robot and a rocket-powered pogo stick, and rode a unicycle down the corridors at Bell Labs. His master's thesis, showing that Boolean algebra could describe electrical switching circuits, has been called the most important master's thesis of the century and is the reason computers are built from logic gates.