Hard disk drive interface

Bridge circuitry is sometimes used to connect hard disk drives to buses with which they cannot communicate natively, such as IEEE 1394, USB, SCSI, NVMe and Thunderbolt.

Thus each time the internal technology advanced there was a necessary delay as controllers were designed or redesigned to accommodate the advancement; this along with the cost of controller development led to the introduction of Word serial interfaces.

Historical Word serial interfaces connect a hard disk drive to a bus adapter[b] with one cable for combined data/control.

The word nature of data transfer makes the design of a host bus adapter significantly simpler than that of the precursor HDD controller.

Modern bit serial interfaces connect a hard disk drive to a host bus interface adapter (today in a PC typically integrated into the "south bridge") with one data/control cable.