Hard Drive Interfaces

The hard disk cannot communicate directly with the CPU or itself. For the hard disk to communicate with the computer, it depends on two more components.  

                                                           

The Controller, which links the drive to the computer

 Host Bus adapter, which converts the signals used by the hard drive to those used and understood by the computer.

ST-506

The ST-506 was the original IBM PC interface. There have two cables, the both cables were used to connect the hard disk to separate controller.

A 20-pin data cable and 34-pin data control cable. The data was transferred on the cable via a serial format one bit at a time. This interface supports the MFM, RLL and ARLL encoding mode of procedure.

ESDI

The ESDI interface was actually a hybrid ST-506 but was more capable in translating and transferring the data. The ESDI interface used the RLL encoding scheme. The ESDI interface also supported much larger drive capacities than that of the old ST-506 interface. Most of these drives were efficient in storing one or more gigabit of data. The interface used the same type of 20-pin data cable and the 34-pin control cable as the ST-506.

ESDI developed on ST-506/ST-412 in many ways. ESDI moved some drive controller functions to the hard disk from the controller card, eliminating some of the reliability errors associated with its predecessor. It had a maximum theoretical bandwidth of 24 Mbits/second (fairly fast for those days), though in practice the limit was about half of that. There were other added features and small performance enhancements as well. Its primary design still had almost all of the intelligence on the controller and not on the hard disk.

IDE

The IDE (also referred to as the AT attachment) was the first interface to actually felt very strongly and difficult to change the controller within the housing of the hard drive itself. Because of the integration of the hard drive and controller in one unit, the cost of the drives also came down. This, along with its improved performance, has made the IDE drive very popular selection for most personal computers sold today. Unlike the ST-506 interface and the ESDI interface. The IDE interface only requires a single 40-pin control and data cable which connects the hard drive to the actual system board.

EIDE

An EIDE host adapter is usually a combination of an EIDE host adapter channel, which can help two drives, and an older IDE host adapter channel, which can support two additional drives. The IDE interface supports two drives physically attached to the same cable, but one drive must be configured as the master and the other as a slave. This is done by setting the device that is directly controlled by second hard drive. The main drive then performs the single and change for both drives. A failure to the main drive gives help to the device directly controlled by another one useless or inaccessible as well.