Serial ATA (SATA)

Serial ATA (SATA), or serial advanced technology attachment, is an integrated drive electronics (IDE) standard for connecting storage devices such as hard drives and optical drives to a computer's motherboard. In general, the term SATA is used in reference to any cables and connections that conform to this standard. After it was initially released in 2001, SATA largely replaced parallel ATA (PATA) as the IDE standard of choice for bridging connections between different computer storage devices. By reducing the number of wires needed to transmit data between a host and a storage device and thereby increasing the speed of such transmissions, SATA provided a superior alternative to PATA connections that quickly became an industry standard. Over the years since this technology's debut, several revisions designed to improve the performance of SATA interfaces have been introduced. The most notable of these included the introduction of SATA Express (SATAe), an external version of SATA used to connect devices located outside the computer itself.

Brief History

The history of SATA can be traced back to the early development of PATA in the late twentieth century. That development began in the mid-1980s with Compaq Computer, a company that primarily specialized in making portable computers. Compaq originally based its designs on that of the IBM personal computer (PC) and the IBM PC-AT, which featured a series of hard disk controller cards that were directly connected to the PC expansion bus—in computer systems, a bus is a shared digital pathway between resources and devices—and whatever disk drives were installed on a given machine. To make smaller and lighter computers that were more realistically portable, Compaq created the Portable II design, which eliminated much of the bulkiness of IBC PC and IBM PC-AT designs by incorporating most of the system's input/output (IO) functions directly onto the motherboard, or the printed circuit board that contains the principal components of a computer. The Portable II design also did away with the idea of having hard disk controller cards being connected directly to the expansion bus, instead of relocating them outside the drive. This design consequently required Compaq to find another way of connecting each controller card to the expansion bus. The solution to this problem was the implementation of an interface circuit-equipped ribbon cable that could connect a card to the bus. After Compaq later began incorporating controller cards inside disc housing drives, these devices became known as integrated disc electronics (IDE) drives. Before long, a wide variety of manufacturers began making their own IDE drives. Because different manufacturers made IDE drives and cables differently, compatibility issues soon became a major problem. This, in turn, led to the need for the development of a standard for implementing IDE hardware. Eventually, a special working group formed to address this problem created the -AT-Attachment (ATA) specification, which formally established a standard interface specification for connections between expansion buses and IDE drives. Because IDE drives and cables used parallel interfaces at the time, this technology became known as parallel ATA (PATA). By the early twenty-first century, faster and more efficient serial interfaces were supplanting parallel interfaces in many computer systems. As a result, a new IDE standard that featured serial interfaces in place of traditional parallel interfaces was introduced in 2001. With that, SATA was born.

Overview

Although it serves essentially the same purpose, SATA differs from PATA in a number of key ways. The most obvious way SATA differs from PATA is in its physical appearance. The PATA standard utilized wide, ribbon-like 80-wire cables and 40-pin connectors. SATA cables, on the other hand, use much thinner 7-wire cables and 7-pin connectors. Because of their smaller size, SATA cables are more manageable, take up less space, and allow for better airflow inside a computer than PATA cables. SATA cables can also be longer than PATA cables. As a result, SATA cables afford computer designers greater freedom in terms of system layout. Since SATA cables have fewer conductors than PATA cables, there is less of a chance of electromagnetic interference or crosstalk, which is the unintended transfer of signals between different communication channels. Unlike PATA, SATA also allows users to hot swap devices. Hot swapping is the ability to replace a device without having to shut down the whole system.

The other most significant difference between SATA and PATA cables is the way in which each type of cable transmits data. Each of PATA's numerous parallel wires were capable of transmitting data simultaneously, meaning that a considerable amount of data could be transmitted at once. While SATA's serial connections can only transfer data one data bit at a time across a single wire, the SATA cable yields a higher signaling rate, which means that the data is ultimately transferred at a faster, more efficient rate.

The SATA standards have been revised a number of times since they were first introduced in 2001. The original SATA devices, which are also referred to as Revision 1, were configured from PATA drives daisy-chained together and offered a transfer rate of 1.5 gigabits per second (Gbps). With the addition of port multipliers, port selectors, and improved queuing introduced in 2004's Revision 2, the transfer speed of SATA devices increased to 3.2 Gbps. SATA transfer speeds increased again to 6 Gbps with the introduction of Revision 3 interfaces in 2009. Revision 3 interfaces also offered backward compatibility with earlier Revision 1 and 2 devices. Later, Revision 3.1 added important design requirements needed to make SATA more compatible with various consumer-based storage applications. The most notable SATA update, however, was 2013's Revision 3.2, which introduced a new specification called SATA Express (SATAe). SATAe allows users to attach external drives to their computers using a SATA connection. On SATAe enabled computers, an external SATA drive can be connected through a SATA port on the back of the computer that connects to the motherboard on the inside. SATA ports rarely come preinstalled on computers, however, and usually must be installed by the user. Most external SATA devices also require the use of an external power source because the wire with which they are equipped is strictly meant for transferring data. In addition to external SATA devices, there are also small form-factor SATA solid-state drives (SSDs) that can be used like standard USB flash drives. These devices are referred to as mSATA.

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