H

Heartbeat

Message that is sent regularly by the Cluster Service on one node to the Cluster Service on an alternate node to maintain communication and detect failure.

Host adapter

Circuitry that translates between a processor's internal bus and a different bus, such as a SCSI. On the SCSI bus, a host acts as an initiator and the peripheral acts as the target.

Hub

Central connecting device in a network that joins communications lines together in a star configuration.