Serial ATA (Serial Advanced Technology Attachment or SATA) is a standard for connecting and transferring data from hard disk drives (HDDs) to computer systems. As its name implies, SATA is based on serial signaling technology, unlike Integrated Drive Electronics (IDE) hard drives that use parallel signaling.
SATA has several advantages over the Parallel ATA (PATA) hard drives developed in the 1980s. SATA cables are thinner, more flexible and less massive than the ribbon cables required for conventional PATA hard drives.
Setting SATA controller modes
Serial ATA hard drives connect to a computer's motherboard via SATA controller hardware that manages the flow of data. Putting SATA in IDE mode means the hard drive is recognized as a PATA device -- a situation that provides better compatibility with older hardware, but comes with the tradeoff of lower performance.
Setting a SATA controller to Advanced Host Controller Interface (AHCI) offers higher performance than IDE mode, and also enables features such as hot swapping on SATA drives. The redundant array of independent disk (RAID) mode supports both AHCI functions and RAID data protection features.
Technical differences between SATA and PATA
The SATA transport layer differs from PATA drives, in which data bits are delivered simultaneously across a 40-pin-wide ribbon cable. As its name suggests, a Serial ATA drive transfers data in serial fashion. Data is moved one bit at a time between a SATA drive and its host, using a seven-pin data cable and 15-pin power cable. The SATA cable results in a higher signaling rate, which corresponds to faster throughput of data.
SATA cables can be considerably longer than PATA ribbon cables, allowing a system designer more latitude in the physical layout of a system. Because there are fewer conductors, the risk of crosstalk and electromagnetic interference is lower. The signal voltage is much lower as well: 250 millivolts for SATA vs. 5 volts for PATA.
SATA standards and revisions
The technical specifications governing Serial ATA device interfaces are authored by the nonprofit SATA-IO industry consortium. The consortium has made several revisions to SATA standards to reflect increased data transfer rates.
- SATA Revision 1 devices were widely used in personal desktop and office computers, configured from PATA drives daisy chained together in a master/slave configuration. SATA Revision 1 devices topped out at a transfer rate of 1.5 gigabits per second (Gbps).
- SATA Revision 2 devices doubled the transfer speed to 3.2 Gbps with the inclusion of port multipliers, port selectors and improved queuing.
- SATA Revision 3 interfaces support drive transfer rates up to 6 Gbps. SATA Revision 3 drives are backward-compatible with SATA Revision 1 and SATA Revision 2 devices, albeit with a lower transfer speed.
- SATA Revision 3.1 is an intermediate revision that added final design requirements for SATA Universal Storage Module for consumer-based portable storage applications.
- SATA Revision 3.2 added a specification known as SATA Express (SATAe), which supports simultaneous use of SATA ports and PCI Express (PCIe) lanes.
SATA design specs for flash storage
In 2009, the SATA-IO consortium unveiled the mSATA specification for small form-factor solid-state drives (SSDs). The M originally stood for mini, but that designation is no longer made and the specification is referred to as mSATA. An mSATA device is a flash drive that conforms to the SATA-IO protocol specification and is mainly used in laptops, netbooks and other portable computing devices. The mSATA specification maps Serial ATA signals to an internally mounted PCIe card in a computer's motherboard.
The emerging M.2 SSD form factor is for ultrathin computing devices; it is generally considered to be an eventual replacement for mSATA.
SATA compared to other storage protocols
SATA drives emerged initially as a method of near-line storage and high-performance secondary storage. Historically, Serial ATA has been viewed as a less costly alternative than Fibre Channel (FC)-based storage area networks built to handle block storage. Advancements in SATA technology have helped narrow the gap with FC, particularly relating to SATA's performance reliability.
Like its SATA counterpart, serial-attached SCSI (SAS) employs thin cables to serially transmit data. SAS historically has been used by enterprises running large-scale storage, particularly to support direct-attached storage or hard drive controllers for enterprise server farms. Some experts predict SAS could overtake SATA as the dominant interface for SSDs and HDDs in enterprise storage systems.