There are various interfaces through which hard disks connect to the computer.
Legacy Bit Serial Interfaces: They are the oldest form of interfaces which used two cables to connect the disk to a controller. One cable was used for data whereas the other is used for control. In addition to the above cables a power cable was also required to provide power to the disk.
Modern Bit Serial Interfaces: In these types of interfaces the disk is connected to a host bus interface adapter using a single cable. In addition to this cable a power cable is also used to power the drive. Some of the modern bit serial interfaces are as follows: Fibre Channel, Serial ATA and SCSI.
World Serial interfaces: They are similar to modern bit interfaces, these interfaces make use of a cable for data and control. Some of the common world interfaces are as follows: IDE, EIDE, SCSI etc.