An interface is a system which can transfer data from one component (or subsystem) to another. An interface connects two components (e.g. a hard disk and a motherboard). Interfaces are responsible for the exchange of data between two components. At the physical level they consist of both software and hardware elements. An interface can consist of controllers with built-in software, cables, etc. Interfaces are typically referred to by their standard or specification, which can cause some confusion.

Parallel Advanced Technology Attachment (PATA)

• Commonly refered to as Integrated Drive Electronics (IDE)
• 16-bit parallel bus width
• Came in 16, 33, 66, 100, 133 MBps throughputs
• IDE through UltraATA/33 has 40 wire cables UltraATA/66-133 has 80 wire cables
• PATA/IDE devices have cable selection jumpers that are used to identify the part of the IDE ribbon cable occupied by a device. Jumpers are necessary in order for the PATA/IDE controller to differentiate between different devices on a single ribbon cable. The options are master, slave, and cable select.
• A typical PC PATA/IDE controller has two channels with each channel able to accommodate two devices on one cable–master and slave; therefore up to 4 devices can be connected to one PATA/IDE controller.

Serial Advanced Technology Attachment (SATA)

• Uses a 1-bit serial bus
• Typical bandwidths are 1.5, 3.0, and 6.0 Gbps
• Uses a special SATA power connector (Molex to SATA converters exist)
• Only one device per SATA connector unless a port multiplexer (SATA Hub) is used
• External support via eSATA port
• Hot-pluggable

Advanced Host Configuration Interface (AHCI)

• A hardware mechanism that allows software to communicate with Serial ATA (SATA) devices that are designed to offer features not offered by Parallel ATA (PATA) controllers, such as hot-plugging and native command queuing
• The operating system, BIOS, and SATA controller must support AHCI
• SATA controllers run in IDE emulation mode when AHCI is unsupported or disabled

Advanced Technology Attachment Packet Interface (ATAPI)

• An enhancement to the protocol (software) section of the ATA interface specification that enabled other devices besides hard drives to connect via the PATA/IDE interface (optical, tape, etc. drives)

Small Computer Systems Interface (SCSI)