heartbeat

1. networking The signal emitted by a Level 2 Ethernet

transceiver at the end of every packet to show that the

collision-detection circuit is still connected.

2. A periodic synchronisation signal used by software or

hardware, such as a bus clock or a periodic interrupt.

3. The "natural" oscillation frequency of a computer's clock

crystal, before frequency division down to the machine's clock

rate.

4. A signal emitted at regular intervals by software to

demonstrate that it is still alive. Sometimes hardware is

designed to reboot the machine if it stops hearing a

heartbeat. See also breath-of-life packet, watchdog.

[Jargon File]

(1996-03-12)