(n.) A greater level of availability typically due to component redundancy. Typically, HA refers to a failover cluster environment in which a service is provided by a primary server until a failure causes that service to be failed over to a secondary server that then becomes the primary server.
horizontal scaling
(n.) Typified as achieving scaling and resilience through replication of a service component (for example, a web server or application server). For scaling to be effective, the workload, or data processed by the service component, should be partitionable. This contrasts with vertical scaling.
See also [vertical scaling]
HVAC
(abb.) Heating, ventilation, and air control
hypervisor
(n.) A virtual machine layer, typically within IBM servers, that enables a single computer to host multiple operating system instances concurrently. A hypervisor is different from dynamic system domains in that it is software or firmware based and acts as an operating system spanning the complete computer.
