Half duplex refers to a communications device or channel that allows alternating transmission and reception, but not both simultaneously.
This contrasts with full duplex, which refers to systems that allow simultaneous transmission and reception. A simplex circuit allows communication only in a single direction.
A walkie-talkie is a half duplex device because only one party can transmit at a time. In contrast, a telephone is a full duplex device because both parties can talk simultaneously.
Some modems contain a switch that lets the user select between half duplex and full duplex modes. The appropriate choice depends on which program is being used to transmit data through the modem.
Created October 23, 2005.