A plug-in board or circuitry on the motherboard acting as the interface between a computer system bus and the drive. Typically used with embedded controller drives, such as SCSI and IDE.
The controller that routes data to and/ or from the CPU.
An adapter that provides connectivity with an expansion bus. A host adapter is different from a "controller" as it simply acts as a go-between, the controller actually resides on the device. An IDE "controller" is actually a host adapter.