Logic circuits include such devices as latches, transceiver, multiplexers, registers, ALUs, and computer memory, all the way up through complete microprocessors which can contain more than a 100 million gates. In practice, the gates are made from FETs, particularly MOSFETs.
Specialty logic gates have diverse states of the output: high (H), low (L) and high-impedance (Z). The high-impedance state plays no role in the logic, which remains strictly binary. These devices are used on buses to allow multiple chips to send data. A group of three-states driving a line with a suitable control circuit is basically equivalent to a multiplexer, which may be physically distributed over separate devices.
Minimized signal distortion during live insertion or withdrawal
High-impedance state during power up and power down
No power-up sequencing required and power-off protection