Bits, Signals, and Buses

A bit is a single 0 or 1 — the smallest unit of information in a digital circuit. A signal is a named, single-wire value that carries one bit through the circuit; giving wires names is what lets you reason about a design instead of a tangle of connections.

A bus is a group of related signals you read together as one value, such as a 4-bit input written in[3:0]. Engineers usually write bus values in hexadecimal because one hex digit stands for exactly four bits, so the binary 1010 is shorter to read and write as the hex digit a.

When a later lesson shows an input like in[3:0] or asks you to read a value in hex, it is using this vocabulary. Bit, signal, bus, and hexadecimal notation recur throughout the course.