Glossary H
Half-Duplex: One way at a time data communication; both devices can transmit and receive data, but only one at a time.

Handshake: An interface procedure that is based on status/data signals that assure orderly data transfer as opposed to asynchronous exchange.

Hardcopy: Output in a permanent form (usually a printout) rather than in temporary form, as on disk or display terminal.

Hardware: The electrical, mechanical and electromechanical equipment and parts associated with a computing system, as opposed to its firmware or software.

Harmonic: A sinusoidal component of a waveform that is a whole multiple of the fundamental frequency. An oscillation that is an integral sub-multiple of the fundamental is called a sub-harmonic.

Heat Sink: 1. Thermodynamic. A body which can absorb thermal energy. 2. Practical. A finned piece of metal used to dissipate the heat of solid state components mounted on it.

Henry: The electromagnetic unit of inductance. 1 Henry occurs when a back emf of 1 volt is produced when current is changing at the rate of 1 amp per second.

Hertz (Hz): Units in which frequency is expressed. Synonymous with cycles per second.

Hexadecimal: Refers to a base sixteen number system using the characters 0 through 9 and A through F to represent the values. Machine language programs are often written in hexadecimal notation.

Hysteresis: The difference in output when the measurand value is first approached with increasing and then with decreasing values. Expressed in percent of full scale during any one calibration cycle. See also Deadband.