Advanced Host Controller Interface (AHCI) is a technical standard that specifies the operation of Serial ATA (SATA) host bus adapters
Serial ATA, SATA or S-ATA (acronym for Serial AT Attachment) is a technology for transferring data between a computer and mass storage devices such as hard drives and optical drives.
It is the successor of ATA technology (acronym for AT Attachment, introduced in 1984 by IBM in their AT computer. ATA, also known as IDE or Integrated Drive Electronics) which was renamed Parallel ATA (PATA) to distinguish it from SATA.
Unlike IDE hard disks, which transmit data via cable forty or eighty parallel wires, resulting in a huge cable, SATA hard drives transfer data in series. Serial ATA cables are formed by two pairs of wires (one pair to another pair for transmission and reception) using differential transmission, and three ground wires, totaling seven wires, which allows to use smaller diameter cables that do not interfere ventilation of the cabinet.
The main advantages over the parallel ATA interface are: high speed transfer of data, ability to remove or add devices while in operation (hot swapping) and using thinner cables allowing cooling air more efficiently.