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Serial ATA (SATA)

The serial ATA (serial advanced technology attachment), or SATA computer bus, is a storage-interface for connecting host bus adapters to mass storage devices such as hard disk drives and optical drives. The SATA host adapter is integrated into almost all modern consumer laptop computers and desktop motherboards.

Serial ATA was designed to replace the older ATA (AT Attachment) standard (also known as EIDE). It is able to use the same low level commands, but serial ATA host-adapters and devices communicate via a high-speed serial cable over two pairs of conductors. In contrast, the parallel ATA (the redesignation for the legacy ATA specifications) used 16 data conductors each operating at a much lower speed.

SATA offers several compelling advantages over the older parallel ATA (PATA) interface: reduced cable-bulk and cost (reduced from forty wires to seven), faster and more efficient data transfer, and hot swapping.

As of 2009, SATA has mostly replaced parallel ATA in all shipping consumer PCs. PATA remains in industrial and embedded applications dependent on CompactFlash storage although the new CFast storage standard will be based on SATA.

SATA specification bodies

There are at least four bodies with possible responsibility for providing SATA specifications: the trade organisation, SATA-IO; the INCITS T10 subcommittee (SCSI); a subgroup of T10 responsible for SAS; and the INCITS T13 subcommittee (ATA). This has caused confusion as the ATA/ATAPI-7 specification from T13 incorporated an early, incomplete SATA rev. 1 specification from SATA-IO. The remainder of this article will try to use the terminology and specifications of SATA-IO.



All SATA devices support hotplugging. However, proper hotplug support requires the device be running in its native command mode not via IDE emulation, which requires AHCI (Advanced Host Controller Interface). Some of the earliest SATA host adapters were not capable of this and furthermore some older operating systems, such as Windows XP, do not directly support AHCI.

Advanced Host Controller Interface

As their standard interface, modern SATA controllers use the AHCI (Advanced Host Controller Interface), allowing advanced features of SATA such as hotplug and native command queuing (NCQ). If AHCI is not enabled by the motherboard and chipset, SATA controllers typically operate in "IDE emulation" mode which does not allow features of devices to be accessed if the ATA/IDE standard does not support them.

Windows device drivers that are labeled as SATA are usually running in IDE emulation mode unless they explicitly state that they are AHCI mode or in RAID mode. While the drivers included with Windows XP do not support AHCI, AHCI has been implemented by proprietary device drivers.[5] Windows Vista, Windows 7, FreeBSD, Linux with kernel version 2.6.19 onward,as well as Solaris and OpenSolaris have native support for AHCI.


The current SATA specifications detail data transfer rates as high as 6.0 Gbit/s per device.

SATA Revision 1.0 (SATA 1.5Gb/s)

First-generation SATA interfaces, now known as SATA 1.5 Gbit/s, communicate at a rate of 1.5 Gbit/s. Taking 8b/10b encoding overhead into account, they have an actual uncoded transfer rate of 1.2 Gbit/s. The theoretical burst throughput of SATA 1.5 Gbit/s is similar to that of PATA/133, but newer SATA devices offer enhancements such as NCQ which improve performance in a multitasking environment.


As of April 2009 mechanical hard disk drives can transfer data at up to 131 MB/s,which is within the capabilities of the older PATA/133 specification. However, high-performance flash drives can transfer data at up to 201 MB/s. SATA 1.5 Gbit/s does not provide sufficient throughput for these drives.

During the initial period after SATA 1.5 Gbit/s finalization, adapter and drive manufacturers used a "bridge chip" to convert existing PATA designs for use with the SATA interface.Bridged drives have a SATA connector, may include either or both kinds of power connectors, and generally perform identically to their PATA equivalents. Most lack support for some SATA-specific features such as NCQ. Bridged products gradually gave way to native SATA products.

Soon after the introduction of SATA 1.5 Gbit/s, a number of shortcomings emerged. At the application level many early SATA host bus adapters could handle only one pending transaction at a time like PATA host bus adapters because they were only capable of operating in IDE emulation mode due to the lack of a standardized interface to utilize SATA's advanced features like native command queuing, which allows drives to reorder commands without creating much CPU utilization, and hot-plugging support. This forced vendors to either develop proprietary solutions and drivers to expose these features, or to omit implementing these features and have the host bus adapter look like a parallel ATA host bus adapter to the operating system. Further compounding this problem was the fact that drives using bridge chips to interface the SATA bus to a PATA drive could not use native command queuing and therefore could only offer the legacy parallel ATA version of tagged command queuing, which drove CPU utilization to impractical levels due to its need to remain software compatibility with its ISA heritage, causing it to be nearly worthless and therefore was almost never implemented. The host bus adapter side of the problem was solved by the introduction of AHCI, which allowed OS vendors to develop a standardized driver for any compliant AHCI SATA host bus adapter to expose these advanced features. The drive side of the problem can be solved by checking to see if a hard drive advertises native command queuing when shopping for a hard drive. Drives that do not advertise this feature or list this feature in their documentation might be drives using a bridge chip and therefore cannot support native command queuing.

SATA Revision 2.0 (SATA 3Gb/s)

First-generation SATA devices often operated at best a little faster than parallel ATA/133 devices. Subsequently, a 3 Gbit/s signaling rate was added to the physical layer (PHY layer), effectively doubling maximum data throughput from 150 MB/s to 300 MB/s.

For mechanical hard drives, SATA 3 Gbit/s transfer rate is expected to satisfy drive throughput requirements for some time, as the fastest mechanical drives barely saturate a SATA 1.5 Gbit/s link. A SATA data cable rated for 1.5 Gbit/s will handle current mechanical drives without any loss of sustained and burst data transfer performance. However, high-performance flash drives are approaching SATA 3 Gbit/s transfer rate.

Given the importance of backward compatibility between SATA 1.5 Gbit/s controllers and SATA 3 Gbit/s devices, SATA 3 Gbit/s autonegotiation sequence is designed to fall back to SATA 1.5 Gbit/s speed when in communication with such devices. In practice, some older SATA controllers do not properly implement SATA speed negotiation. Affected systems require the user to set the SATA 3 Gbit/s peripherals to 1.5 Gbit/s mode, generally through the use of a jumper, however some drives lack this jumper. Chipsets known to have this fault include the VIA VT8237 and VT8237R southbridges, and the VIA VT6420, VT6421A and VT6421L standalone SATA controllers.SiS's 760 and 964 chipsets also initially exhibited this problem, though it can be rectified with an updated SATA controller ROM.

SATA II misnomer

Popular usage refers to the SATA 3 Gbit/s specification as Serial ATA II (SATA II or SATA2), contrary to the wishes of the Serial ATA International Organization (SATA-IO) which defines the standard. SATA II was originally the name of a committee defining updated SATA standards, of which the 3 Gbit/s standard was just one. However since it was among the most prominent features defined by the former SATA II committee, and, more critically, the term "II" is commonly used for successors, the name SATA II became synonymous with the 3 Gbit/s standard, so the group has since changed names to the Serial ATA International Organization, or SATA-IO, to avoid further confusion.

As of 2009, "SATA II" and "SATA 2" are the most common marketing terms for any "second-generation" SATA drives, controllers or related accessories. Unfortunately, these terms have no specific meaning, since they are not the proper official nomenclature. Also, the second-generation SATA standards only define a set of optional features (3 Gb/s, NCQ — Native Command Queuing, staggered spin-up and hot-plugging) improving on the first generation technology, but don't require including those features. Almost any SATA product with any set of features could legitimately be described as "compatible" with these standards. Only careful research can determine which features may be included in any particular "SATA II" product.

In order to avoid parallels to the common SATA II misnomer, the SATA-IO has compiled a set of marketing guidelines for the third revision of the specification. The specification should be called Serial ATA International Organization: Serial ATA Revision 3.0, and the technology itself is to be referred to as SATA 6Gb/s. A product using this standard should be called the SATA 6Gb/s [product name]. The terms SATA III or SATA 3.0, which are considered to cause confusion among consumers, must not be used. Engadget uses the term SATA 6G. This may cause confusion since SATA 6 GBit/s is the third generation of SATA. Generation is often shortened to just G as in the cellular technology 3G.

 SATA Revision 3.0 (SATA 6Gb/s)

Serial ATA International Organization presented the draft specification of SATA 6 Gbit/s physical layer in July 2008, and ratified its physical layer specification on August 18, 2008.The full 3.0 standard was released on May 27, 2009.While even the fastest conventional hard disk drives can barely saturate the original SATA 1.5 Gbit/s bandwidth, Solid State Disk drives have already saturated the SATA 3 Gbit/s limit at 250 MB/s net read speed. Ten channels of fast flash can reach well over 500 MB/s with new ONFI drives, so a move from SATA 3 Gbit/s to SATA 6 Gbit/s would benefit the flash read speeds. As for the standard hard disks, the reads from their built-in DRAM cache will end up faster across the new interface.Seagate was the first company to offer SATA 6 Gbit/s hard drives.

The new specification contains the following changes:

  • A new Native Command Queuing (NCQ) streaming command to enable Isochronous data transfers for bandwidth-hungry audio and video applications.
  • An NCQ Management feature that helps optimize performance by enabling host processing and management of outstanding NCQ commands.
  • Improved power management capabilities.
  • A small Low Insertion Force (LIF) connector for more compact 1.8-inch storage devices.
  • A connector designed to accommodate 7 mm optical disk drives for thinner and lighter notebooks.
  • Alignment with the INCITS ATA8-ACS standard.

The enhancements are generally aimed at improving quality of service for video streaming and high priority interrupts. In addition, the standard continues to support distances up to a meter. The new speeds may require higher power consumption for supporting chips, factors that new process technologies and power management techniques are expected to mitigate. The new specification can use existing SATA cables and connectors, although some OEMs are expected to upgrade host connectors for the higher speeds.Also, the new standard is backwards compatible with SATA 3 Gbit/s.

External SATA


The official eSATA logo


eSATA, standardized in 2004, provides a variant of SATA meant for external connectivity. It has revised electrical requirements in addition to incompatible cables and connectors:

  • Minimum transmit potential increased: Range is 500–600 mV instead of 400–600 mV.
  • Minimum receive potential decreased: Range is 240–600 mV instead of 325–600 mV.
  • Identical protocol and logical signaling (link/transport-layer and above), allowing native SATA devices to be deployed in external enclosures with minimal modification
  • Maximum cable length of 2 metres (6.6 ft) (USB and FireWire allow longer distances.)
  • The external cable connector equates to a shielded version of the connector specified in SATA 1.0a with these basic differences:
    • The external connector has no "L" shaped key, and the guide features are vertically offset and reduced in size. This prevents the use of unshielded internal cables in external applications and vice-versa.
    • To prevent ESD damage, the design increased insertion depth from 5 mm to 6.6 mm and the contacts are mounted farther back in both the receptacle and plug.
    • To provide EMI protection and meet FCC and CE emission requirements, the cable has an extra layer of shielding, and the connectors have metal contact-points.
    • The connector shield has springs as retention features built in on both the top and bottom surfaces.
    • The external connector and cable have a design-life of over five thousand insertions and removals, while the internal connector is only specified to withstand fifty.
SATA (left) and eSATA (right) connectors

Aimed at the consumer market, eSATA enters an external storage market already served by the USB and FireWire interfaces. Most external hard-disk-drive cases with FireWire or USB interfaces use either PATA or SATA drives and "bridges" to translate between the drives' interfaces and the enclosures' external ports, and this bridging incurs some inefficiency. Some single disks can transfer 131 MB/s during real use, about four times the maximum transfer rate of USB 2.0 or FireWire 400 (IEEE 1394a) and almost twice as fast as the maximum transfer rate of FireWire 800, though the S3200 FireWire 1394b spec reaches ~400 MB/s (3.2 Gbit/s). Finally, some low-level drive features, such as S.M.A.R.T., may not operate through USB or FireWire bridging. eSATA does not suffer from these issues provided that the controller manufacturer (and its drivers) presents eSATA drives as ATA devices, rather than as "SCSI" devices (as has been common with Silicon Image, JMicron, and NVIDIA nForce drivers for Windows Vista); In those cases, even SATA drives will not have low-level features accessible. USB 3.0's 4.8Gbit/s and Firewire's future 6.4Gb/s will be faster than eSATA I, but the eSATA version of SATA 6G (the term SATA III is being eschewed by the SATA-IO to avoid confusion with SATA II 3.0 Gb/s which was colloquially referred to as "SATA 3G" [bps] or "SATA 300" [MB/s] since 1.5 Gb/s SATA I and 1.5 Gb/s SATA II were referred to as both "SATA 1.5G" [b/s] or "SATA 150" [MB/s]) will operate at 6.0Gb/s, thereby operating at negligible differences of each other.

eSATA can be differentiated from USB 2.0 and FireWire external storage for several reasons. As of early 2008, the vast majority of mass-market computers have USB ports and many computers and consumer electronic appliances have FireWire ports, but few devices have external SATA connectors. For small form-factor devices (such as external 2.5-inch disks), a PC-hosted USB or FireWire link supplies sufficient power to operate the device. Where a PC-hosted port is concerned, eSATA connectors cannot supply power, and would therefore be more cumbersome to use.

Owners of desktop computers that lack a built-in eSATA interface can upgrade them with the installation of an eSATA host bus adapter (HBA), while notebooks can be upgraded with Cardbus or ExpressCardversions of an eSATA HBA. With passive adapters the maximum cable length is reduced to 1 metre (3.3 ft) due to the absence of compliant eSATA signal-levels. Full SATA speed for external disks (115 MB/s) have been measured with external RAID enclosures.

 Pre-standard implementations

Prior to the final eSATA specification, a number of products existed designed for external connections of SATA drives. Some of these use the internal SATA connector or even connectors designed for other interface specifications, such as FireWire. These products are not eSATA compliant. The final eSATA specification features a specific connector designed for rough handling, similar to the regular SATA connector, but with reinforcements in both the male and female sides, inspired by the USB connector. eSATA resists inadvertent unplugging, and can withstand yanking or wiggling which would break a male SATA connector (the hard-drive or host adapter, usually fitted inside the computer). With an eSATA connector, considerably more force is needed to damage the connector, and if it does break it is likely to be the female side, on the cable itself, which is relatively easy to replace.

Cables, connectors, and ports

Connectors and cables present the most visible differences between SATA and parallel ATA drives. Unlike PATA, the same connectors are used on 3.5-inch SATA hard disks for desktop and server computers and 2.5-inch disks for portable or small computers; this allows 2.5-inch drives to be used in desktop computers with only a mounting bracket and no wiring adapter. Smaller disks may use the mini-SATA spec, suitable for small-form-factor Serial ATA drives and mini SSDs.

There is a special connector (eSATA) specified for external devices, and an optionally implemented provision for clips to hold internal connectors firmly in place. SATA drives may be plugged into SAS controllers and communicate on the same physical cable as native SAS disks, but SATA controllers cannot handle SAS disks.

There are SATA ports (on motherboards of a PC) that can use SATA data cable with locks or clips, thus, reducing the chance of accidentally unplugging while the PC is turned on. So does the same with SATA power connector and SATA data connector connected to a SATA HDD or SATA optical drive. Also, there are right-angled and left-angled connectors only on one end of SATA data cable, which can only be used when connecting to a SATA HDD or SATA optical drive.



Pin # Function
1 Ground
2 A+ (Transmit)
3 A− (Transmit)
4 Ground
5 B− (Receive)
6 B+ (Receive)
7 ground
8 coding notch
A 7-pin Serial ATA data cable.
A 7-pin Serial ATA right-angle data cable.

The SATA standard defines a data cable with seven conductors (3 grounds and 4 active data lines in two pairs) and 8 mm wide wafer connectors on each end. SATA cables can have lengths up to 1 metre (3.3 ft), and connect one motherboard socket to one hard drive. PATA ribbon cables, in comparison, connect one motherboard socket to up to two hard drives, carry either 40 or 80 wires, and are limited to 45 centimetres (18 in) in length by the PATA specification (however, cables up to 90 centimetres (35 in) are readily available). Thus, SATA connectors and cables are easier to fit in closed spaces and reduce obstructions to air cooling. They are more susceptible to accidental unplugging and breakage than PATA, but cables can be purchased that have a locking feature, whereby a small (usually metal) spring holds the plug in the socket.

One of the problems associated with the transmission of data at high speed over electrical connections is loosely described as noise. Despite attempts to avoid it, some electrical coupling will exist both between data circuits and between them and other circuits. As a result, the data circuits can both affect other circuits, whether they are within the same piece of equipment or not, and can be affected by them. Designers use a number of techniques to reduce the undesirable effects of such unintentional coupling. One such technique used in SATA links is differential signaling. This is an enhancement over PATA, which uses single-ended signaling. Twisted pair cabling also gives superior performance in this regard.


 Power supply

 Standard connector

Pin # Mating Function
 — coding notch
  1 3rd 3.3 V
2 3rd
3 2nd
  4 1st Ground
5 2nd
6 2nd
  7 2nd 5 V
8 3rd
9 3rd
  10 2nd Ground
  11 3rd Staggered spinup/activity
(in supporting drives)
  12 1st Ground
  13 2nd 12 V
14 3rd
15 3rd
A 15-pin Serial ATA power connector.
A 15-pin Serial ATA power receptacle. This connector does not
provide the extended pins 4 and 12 needed for hot-plugging.

The SATA standard specifies a different power connector than the decades-old four-pin Molex connector found on pre-SATA devices. Like the data cable, it is wafer-based, but its wider 15-pin shape prevents accidental mis-identification and forced insertion of the wrong connector type. Native SATA devices favor the SATA power-connector, although some early SATA drives retained older 4-pin Molex in addition to the SATA power connector.

SATA features more pins than the traditional connector for several reasons:

  • A third voltage is supplied, 3.3 V, in addition to the traditional 5 V and 12 V.
  • Each voltage transmits through three pins ganged together, because the small contacts by themselves cannot supply sufficient current for some devices. (Each pin should be able to provide 1.5 A.)
  • Five pins ganged together provide ground.
  • For each of the three voltages, one of the three pins serves for hotplugging. The ground pins and power pins 3, 7, and 13 are longer on the plug (located on the SATA device) so they will connect first. A special hot-plug receptacle (on the cable or a backplane) can connect ground pins 4 and 12 first.
  • Pin 11 can function for staggered spinup, activity indication, or nothing. Staggered spinup is used to prevent many drives from spinning up simultaneously, as this may draw too much power. Activity is an indication of whether the drive is busy, and is intended to give feedback to the user through a LED.

Adapters exist which can convert a 4-pin Molex connector to a SATA power connector. However, because the 4-pin Molex connectors do not provide 3.3 V power, these adapters provide only 5 V and 12 V power and leave the 3.3 V lines unconnected. This precludes the use of such adapters with drives that require 3.3 V power. Understanding this, drive manufacturers have largely left the 3.3 V power lines unused.


Slimline connector

SATA 2.6 first defined the slimline connector, intended for smaller form-factors; e.g., notebook optical drives.

Pin # Function
  1 Device Present
  2 5 V
  4 Manufacturing Diagnostic
  5 Ground

A 6-pin Slimline Serial ATA power connector. Note that pin 1 (device present) is shorter than the others.

 Micro connector

The micro connector originated with SATA 2.6. It is intended for 1.8-inch hard drives. There is also a micro data connector, which is similar to the standard data connector, but is slightly thinner.

Pin # Function
  1 3.3 V
  3 Ground
  5 5 V
  7 Reserved
  8 Vendor Specific




SATA topology: host – expansor - device

SATA uses a point-to-point architecture. The connection between the controller and the storage device is direct.

Modern PC systems usually have a SATA controller on the motherboard, or installed in a PCI or PCI Express slot. Most SATA controllers have multiple SATA ports and can be connected to multiple storage devices. There are also port expanders or multipliers which allow multiple storage devices to be connected to a single SATA controller port.


Physical transmission uses a logic encoding known as 8b/10b encoding. This scheme eliminates the need to send a separate clock signal with the data stream. The stream itself contains necessary synchronization information which allows for SATA host/drive to extract clocking. Use of 8b/10b encoding means the stream is also DC-balanced which allows the signals to be AC-coupled.

Separate point-to-point AC-coupled LVDS links are used for physical transmission between host and drive.

 Backward and forward compatibility


At the device level, SATA and PATA (Parallel Advanced Technology Attachment) devices remain completely incompatible—they cannot be interconnected. At the application level, SATA devices can be specified to look and act like PATA devices. Many motherboards offer a "legacy mode" option which makes SATA drives appear to the OS like PATA drives on a standard controller. This eases OS installation by not requiring a specific driver to be loaded during setup but sacrifices support for some features of SATA and generally disables some of the boards' PATA or SATA ports since the standard PATA controller interface only supports 4 drives. (Often which ports are disabled is configurable.)

The common heritage of the ATA command set has enabled the proliferation of low-cost PATA to SATA bridge-chips. Bridge-chips were widely used on PATA drives (before the completion of native SATA drives) as well as standalone "dongles." When attached to a PATA drive, a device-side dongle allows the PATA drive to function as a SATA drive. Host-side dongles allow a motherboard PATA port to function as a SATA host port.

The market has produced powered enclosures for both PATA and SATA drives which interface to the PC through USB, Firewire or eSATA, with the restrictions noted above. PCI cards with a SATA connector exist that allow SATA drives to connect to legacy systems without SATA connectors.

 SATA 1.5 Gbit/s and SATA 3 Gbit/s

The designers of SATA aimed for backward and forward compatibility with future revisions of the SATA standard.

 Comparisons with other interfaces


SCSI currently offers transfer rates higher than SATA, but it uses a more complex bus, usually resulting in higher manufacturing costs. SCSI buses also allow connection of several drives (using multiple channels, 7 or 15 on each channel), whereas SATA allows one drive per channel, unless using a port multiplier.

SATA 3 Gbit/s offers a maximum bandwidth of 300 MB/s per device compared to SCSI with a maximum of 320 MB/s. Also, SCSI drives provide greater sustained throughput than SATA drives because of disconnect-reconnect and aggregating performance. SATA devices generally link compatibly to SAS enclosures and adapters, while SCSI devices cannot be directly connected to a SATA bus.

SCSI, SAS and fibre-channel (FC) drives are typically more expensive so they are traditionally used in servers and disk arrays where the added cost is justifiable. Inexpensive ATA and SATA drives evolved in the home-computer market, hence there is a view that they are less reliable. As those two worlds overlapped, the subject of reliability became somewhat controversial. Note that, generally, the failure rate of a disk drive is related to the quality of its heads, platters and supporting manufacturing processes, not to its interface.

SATA in comparison to other buses

Name Raw bandwidth (Mbit/s) Transfer speed (MB/s) Max. cable length (m) Power provided Devices per Channel
eSATA 3,000 300 2 with eSATA HBA (1 with passive adapter) No 1 (15 with port multiplier)
eSATAp 5V/12V[28]
SATA 600 6,000 600 1 No
SATA 300 3,000 300
SATA 150 1,500 150 1 per line
PATA 133 1,064 133 0.46 (18 in) No 2
SAS 300 3,000 300 8 No 1 (16k with expanders)
SAS 150 1,500 150
FireWire 3200 3,144 393 100 (more with special cables) 15 W, 12–25 V 63 (with hub)
FireWire 800 786 98.25 100
FireWire 400 393 49.13 4.5
USB 3.0* 5,000 600 3 4.5 W, 5 V 127 (with hub)
USB 2.0 480 60 5 2.5 W, 5 V
USB 1.0 12 1.5 3 Yes
Ultra-320 SCSI 2,560 320 12 No 15 (plus the HBA)
Fibre Channel
over optic fiber
10,520 2,000 2–50,000 No 126
(16,777,216 with switches)
Fibre Channel
over copper cable
4,000 400 12
Quad Rate
10,000 8,000 5 (copper)

<10,000 (fiber)

No 1 with point to point
Many with switched fabric
Light Peak 10,000 1,250 100 No Many

* USB 3.0 specification released to hardware vendors 17 November 2008.

Unlike PATA, both SATA and eSATA support hot-swapping by design. However, this feature requires proper support at the host, device (drive), and operating-system level. In general, all SATA devices (drives) support hot-swapping (due to the requirements on the device-side), also most SATA host adapters support this command.

SCSI-3 devices with SCA-2 connectors are designed for hot-swapping. Many server and RAID systems provide hardware support for transparent hot-swapping. The designers of the SCSI standard prior to SCA-2 connectors did not target hot-swapping, but, in practice, most RAID implementations support hot-swapping of hard disks.