Serial communication

Practically all long-distance communication transmits data one bit at a time, rather than in parallel, because it reduces the cost of the cable.

To reduce the number of pins in a package, many ICs use a serial bus to transfer data when speed is not important.

Some examples of such low-cost lower-speed serial buses include RS-232, DALI, SPI, CAN bus, I²C, UNI/O, and 1-Wire.

A parallel link transmits several streams of data simultaneously along multiple channels (e.g., wires, printed circuit tracks, or optical fibers); whereas, a serial link transmits only a single stream of data.

The rationale for parallel communication was the added benefit of having Direct Memory Access to the 8-bit or 16-bit registry addresses at a time where mapping direct data lanes was more convenient and faster than synchronizing data serially.

Differential signalling uses length-matched wires or conductors and are used in high speed serial links.