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Encyclopedia > SATA
A SATA power connector. A SATA data cable looks the same except it is only 7 pins wide, as opposed to the 15 seen here.
A SATA power connector. A SATA data cable looks the same except it is only 7 pins wide, as opposed to the 15 seen here.

In computer hardware Serial ATA (also SATA or S-ATA) is a computer bus primarily designed for transfer of data to and from a hard disk. It is the successor to the legacy Advanced Technology Attachment standard (ATA, also known as IDE). This older technology is now known as Parallel ATA (PATA) to distinguish it from Serial ATA.

First-generation Serial ATA interfaces have a bandwidth of 150 megabytes per second (MB/s) — or 1.5 gigabits per second (Gbit/s) — only slightly higher than that provided by the fastest PATA mode, UDMA-133. However, while further increasing PATA bandwidth is somewhat impractical, the relative simplicity of a serial link and the use of LVDS should allow SATA to scale easily. Serial ATA II (available as of 2004, with the release of Nvidia nForce4 chipset) doubles the maximum throughput to 300 MB/s (3 Gbit/s), and 600 MB/s (6 Gbit/s) is planned for around 2007. Still, the need for such a high speed interface is currently questionable; the (rarely reached) maximum transfer rates of the fastest magnetic hard drives are currently well under 100 MB/s, and any additional bandwidth benefits only transfers from the disk's cache.

Serial ATA innovations

Physically, the cables used are the most noticeable change. The standard defines a seven-conductor wire with 8 mm wide wafer connectors on each end as the data cable. SATA cables can be up to 1m (40 inches) long. PATA ribbon cables, in comparison, carry either 40 or 80 conductor wires and are limited to 45cm (18 inches) in length. Serial ATA drops the master/slave shared bus of PATA, giving each device a dedicated cable and dedicated bandwidth. Unlike early PATA connectors, SATA connectors are keyed — it is not possible to install cable connectors upside down.

The Serial ATA standard also specifies a power connector sharply differing from the four-pin Molex connector used by PATA drives and many other computer components. Like the data cable, it is wafer based, but its wider fifteen-pin shape should prevent confusion between the two. The seemingly large number of pins are used to supply three different voltages if necessary — 3.3 V, 5 V and 12 V. The same physical connections are used on 3.5 inch and 2.5 inch (notebook) hard disks.

Features allowed for by SATA but not by PATA include hot-swapping and native command queueing.

To ease their transition to Serial ATA, many manufacturers have produced drives which use controllers largely identical to those on their PATA drives and include a bridge chip on the logic board. Bridged drives have a SATA connector, may include either or both kinds of power connectors, and generally perform identically to native drives. They may, however, lack support for some SATA-specific features. As of 2004, all major hard drive manufacturers produce either bridged or native SATA drives.

SATA drives may be plugged into Serial Attached SCSI (SAS) controllers and communicate on the same physical cable as native SAS disks. SAS disks however may not be plugged into a SATA controller.

External links

  • Serial ATA working group specifications (http://www.serialata.org/specifications.asp)
  • Tom's Hardware controller tests (http://www.tomshardware.com/storage/20030204/)
  • Using serial ATA with Linux (http://www.linuxmafia.com/faq/Hardware/sata.html)
  • SATA / SAS / SAN / NAS / Storage Information (http://home.nc.rr.com/woodsmall/SAN-NAS.htm)

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SATA was introduced in 2002 at significantly higher speed, transferring data in each direction at 1.5 Gbps.
SATA cables and connectors are considerably smaller than their PATA counterpart and take up a lot less space in the case.
SATA defines only internal drives, but eSATA (External SATA) enables them to reside in their own housing outside the computer and be plugged in as required.
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