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Serial ATA

Serial ATA (SATA or Serial ) is a computer bus interface for connecting host bus adapters to mass storage devices such as hard disk drives and optical drives. Serial ATA was designed to replace the older parallel ATA (PATA) standard (often called by the old name IDE), offering several advantages over the older interface: reduced cable size and cost (7 conductors instead of 40), native hot swapping, faster data transfer through higher signalling rates, and more efficient transfer through an (optional) I/O queuing protocol.

SATA host-adapters and devices communicate via a high-speed serial cable over two pairs of conductors. In contrast, parallel ATA (the redesignation for the legacy ATA specifications) used a 16-bit wide data bus with many additional support and control signals, all operating at much lower frequency. To ensure backward compatibility with legacy ATA software and applications, SATA uses the same basic ATA and ATAPI command-set as legacy ATA devices.

SATA has replaced parallel ATA in consumer desktop and laptop computers, and has largely replaced PATA in new embedded applications. SATA's market share in the desktop PC market was 99% in 2008.[1] PATA remains widely used in industrial and embedded applications that use CompactFlash storage, though even there, the new CFast storage standard is based on SATA.[2][3]

Serial ATA industry compatibility specifications originate from The Serial ATA International Organization (aka. SATA-IO, serialata.org). The SATA-IO group collaboratively creates, reviews, ratifies, and publishes the interoperability specifications, the test cases, and plug-fests. As with many other industry compatibility standards, the SATA content ownership is transferred to other industry bodies: primarily the INCITS T13 subcommittee ATA, the INCITS T10 subcommittee (SCSI); a subgroup of T10 responsible for Serial Attached SCSI (SAS). The complete specification from SATA-IO.[4] The remainder of this article will try to use the terminology and specifications of SATA-IO.

Contents


Features

Hotplug

The Serial ATA Spec includes logic for SATA device hotplugging. Devices and motherboards that meet the interoperability specification are capable of hot plugging.

Advanced Host Controller Interface

Advanced Host Controller Interface (AHCI) is an open host controller interface published and used by Intel, which has become a de facto standard. It allows the use of 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 often running in IDE emulation mode unless they explicitly state that they are AHCI mode, in RAID mode, or a mode provided by a proprietary driver and command set that was designed to allow access to SATA's advanced features before AHCI became popular. Modern versions of Microsoft Windows, Mac OS X, FreeBSD, Linux with version 2.6.19 onward,[5] as well as Solaris and OpenSolaris, include support for AHCI, but older OSs such as Windows XP do not. Even in those instances, a proprietary driver may have been created for a specific chipset, such as Intel's.[6]

Revisions

SATA revision 1.0 (SATA 1.5 Gbit/s)

First-generation SATA interfaces, now known as SATA 1.5 Gbit/s, communicate at a rate of 1.5 Gbit/s, and do not support NCQ. Taking 8b/10b encoding overhead into account, they have an actual uncoded transfer rate of 1.2 Gbit/s (150 MB/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.

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, in general, perform identically to their PATA equivalents. Most lack support for some SATA-specific features such as NCQ. Native SATA products quickly eclipsed bridged products with the introduction of the second generation of SATA drives.

As of April 2010 the fastest 10,000 RPM SATA mechanical hard disk drives could transfer data at maximum (not average) rates of up to 157 MB/s,[7] which is beyond the capabilities of the older PATA/133 specification and also exceeds a SATA 1.5 Gbit/s link.

SATA revision 2.0 (SATA 3 Gbit/s)

Second generation SATA interfaces running at 3.0 Gbit/s shipped in high volume by 2010, and were prevalent in all SATA disk drives and most PC and server chipsets. With a native transfer rate of 3.0 Gbit/s, and taking 8b/10b encoding into account, the maximum uncoded transfer rate is 2.4 Gbit/s (300 MB/s). The theoretical burst throughput of SATA 3.0 Gbit/s is roughly double that of SATA revision 1.

All SATA data cables meeting the SATA spec are rated for 3.0 Gbit/s and will handle current mechanical drives without any loss of sustained and burst data transfer performance. However, high-performance flash drives exceed the SATA 3 Gbit/s transfer rate; this is addressed with the SATA 6 Gbit/s interoperability standard.

SATA revision 3.0 (SATA 6 Gbit/s)

Serial ATA International Organization presented the draft specification of SATA 6 Gbit/s physical layer in July 2008,[8] and ratified its physical layer specification on August 18, 2008.[9] The full 3.0 standard was released on May 27, 2009.[10] It provides peak throughput of about 600 MB/s (Megabytes per second) including the protocol overhead (10b/8b coding with 10 bits to one byte). The 3.0 specification contains the following changes:

  • 6 Gbit/s for scalable performance
  • Continued compatibility with SAS, including SAS 6 Gbit/s. "A SAS domain may support attachment to and control of unmodified SATA devices connected directly into the SAS domain using the Serial ATA Tunneled Protocol (STP)" from the SATA_Revision_3_0_Gold specification.
  • Isochronous Native Command Queuing (NCQ) streaming command to enable isochronous quality of service data transfers for streaming digital content 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.

In general, the enhancements are aimed at improving quality of service for video streaming and high-priority interrupts. In addition, the standard continues to support distances up to one meter. The newer speeds may require higher power consumption for supporting chips, although improved process technologies and power management techniques may mitigate this. The later specification can use existing SATA cables and connectors, although it was reported in 2008 that some OEMs were expected to upgrade host connectors for the higher speeds.[11]

The later standard is backwards compatible with SATA 3 Gbit/s.[12]

SATA revision 3.1

New:[13]

  • mSATA, SATA for solid-state drives in mobile computing devices, a PCI Express Mini Card-like connector which is electrically SATA[14]
  • Zero-power optical disk drive, idle SATA optical drive draws no power
  • Queued TRIM Command, improves solid-state drive performance
  • Required Link Power Management, reduces overall system power demand of several SATA devices
  • Hardware Control Features, enable host identification of device capabilities
  • Universal Storage Module, a new standard for cableless plug-in (slot) powered storage for consumer electronics devices[15]

SATA revision 3.2

[16]

  • SATA Express
  • SSD

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 SATA hard disks for desktop and server computers and disks for portable or small computers.

Standard SATA connectors for both data and power have a conductor pitch of 1.27 mm (1/20").

A smaller mini-SATA or mSATA connector is used by smaller devices such as 1.8" SATA drives, some DVD and Blu-ray drives, and mini SSDs.[17]

A special eSATA connector is 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.

Female SATA ports (on motherboards for example) are intended to be used with SATA data cables that have locks or clips to reduce the chance of accidental unplugging. Some SATA cables have right-angled connectors to ease the connection of devices to circuit boards.

Data connector

Pin # Mating Function
1 1st Ground
2 2nd A+ (Transmit)
3 2nd A- (Transmit)
4 1st Ground
5 2nd B- (Receive)
6 2nd B+ (Receive)
7 1st Ground
  Coding notch

A 7-pin SATA data cable. SATA connector on a hard drive; data connections on the left and power connections on the right. Note the two different pin lengths used to ensure a specific mating order (especially to ensure that ground pins make contact first). 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 , and connect one motherboard socket to one hard drive. PATA ribbon cables, in comparison, connect one motherboard socket to one or two hard drives, carry either 40 or 80 wires, and are limited to in length by the PATA specification (however, cables up to 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.

SATA connectors may be straight, right-angled, or left angled. Angled connectors allow for lower profile connections. Right-angled (also called 90 degree) connectors lead the cable immediately away from the drive, on the circuit board side. Left-angled (also called 270 degree) connectors lead the cable across the drive towards its top.

One of the problems associated with the transmission of data at high speed over electrical connections is described as noise, which is due to electrical coupling between data circuits and other circuits. As a result, the data circuits can both affect other circuits, and 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. The use of fully shielded twin-ax conductors, with multiple ground connections, for each differential pair improves isolation between the channels and reduces the chances of lost data in difficult electrical environments. SATA-3 Cable showing fully shielded twin-ax pairs

Power connectors

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 SATA power connector. Note that this connector is missing the 3.3V (orange) wire. The SATA standard specifies a power connector that differs from 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. However, nearly all current disk drives do not use the 3.3 V line.
  • Each voltage is transmitted through three pins grouped together, because the small contacts by themselves cannot supply sufficient current for some devices. (Each pin should be able to carry 1.5 A.)
  • Six or five pins provide ground. Six being standard or five if staggered spinup or other special functionality is supported.
  • 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, both, or nothing. It is an open collector signal, that may be pulled down by the connector or the drive. If pulled down at the connector (as it is on most cable-style SATA power connectors), the drive spins up as soon as power is applied. If left floating, the drive waits until it is spoken to, This prevents many drives from spinning up simultaneously, which might draw too much power. The pin is also pulled low by the drive to indicate drive activity. This may be used to give feedback to the user through an LED.

Passive adapters are available that convert a 4-pin Molex connector to a SATA power connector, providing the 5 V and 12 V lines available on the Molex connector, but not 3.3 V. There are also 4-pin-Molex-to-SATA power adapters which include electronics to provide 3.3 V power additionally.[18] However, most drives do not require the 3.3 V power line.

Slimline connector

Pin # Mating Function
  Coding notch
1 3rd Device presence
2 2nd 5 V
3 2nd
4 2nd Manufacturing diagnostic
5 1st Ground
6 1st

A 6-pin Slimline SATA power connector. The back of a SATA-based slimline optical drive. SATA 2.6 first defined the slimline connector, intended for smaller form-factors; e.g., notebook optical drives. Pin 1 (device presence) is shorter than the others.

Micro connector

Pin # Mating Function
1 3rd 3.3 V
2 2nd
3 1st Ground
4 1st
5 2nd 5 V
6 3rd
7 3rd Reserved
  Coding notch
8 3rd Vendor specific
9 2nd

A 1.8-inch (46-millimeter) hard drive, showing data connector and micro power connector. The micro connector originated with SATA 2.6. It is intended for hard drives. There is also a micro data connector, similar in appearance to but slightly thinner than the standard data connector.

eSATA

The official eSATA logo
The official eSATA logo
SATA (left) and eSATA (right) connectors
SATA (left) and eSATA (right) connectors
eSATA receptacles
eSATA receptacles

Standardized in 2004, eSATA (e standing for external) provides a variant of SATA meant for external connectivity. It uses a more robust connector, longer shielded cables, and stricter (but backward-compatible) electrical standards. The protocol and logical signaling (link/transport layers and above) are identical to internal SATA. The differences are:

  • Minimum transmit amplitude increased: Range is 500 600 mV instead of 400 600 mV.
  • Minimum receive amplitude decreased: Range is 240 600 mV instead of 325 600 mV.
  • Maximum cable length increased to (USB and FireWire allow longer distances.)
  • The external cable connector is 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 retention springs on both the top and bottom surfaces.
    • The external connector and cable have a design-life of over five thousand insertions and removals, whereas the internal connector is specified to withstand only fifty.

Aimed at the consumer market, eSATA enters an external storage market served also by the USB and FireWire interfaces. The SATA interface has certain advantages. 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; this bridging incurs some inefficiency. Some single disks can transfer 157 MB/s during real use,[7] 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. The S3200 FireWire 1394b spec reaches ~400 MB/s (3.2 Gbit/s), and USB 3.0 has a nominal speed of 5 Gbit/s. Some low-level drive features, such as S.M.A.R.T., may not operate through some USB [19] or FireWire or USB+FireWire bridges; 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 SATA drives will not have low-level features accessible. Firewire's future 6.4 Gbit/s (768 MB/s) will be faster than eSATA I. The eSATA version of SATA 6G will operate at 6.0 Gbit/s (the term SATA III is being eschewed by the SATA-IO to avoid confusion with SATA II 3.0 Gbit/s, which was colloquially referred to as "SATA 3G" [bps] or "SATA 300" [MB/s] since 1.5 Gbit/s SATA I and 1.5 Gbit/s SATA II were referred to as both "SATA 1.5G" [b/s] or "SATA 150" [MB/s]). Therefore, they will operate with negligible differences between them.[20] Once an interface can transfer data as fast as a drive can handle them, increasing the interface speed does not improve data transfer. Most newer computers, including netbooks/laptops, have external SATA (eSATA) connectors, in addition to USB 2.0 and sometimes USB 3.0 ports, although relatively few have built-in FireWire ports.

There are some disadvantages, however, to the eSATA interface. Devices built before the eSATA interface became popular lack external SATA connectors. For small form-factor devices (such as external disks), a PC-hosted USB or FireWire link can usually supply sufficient power to operate the device. However, eSATA connectors cannot supply power, and require a power supply for the external device. The related eSATAp (but mechanically incompatible, sometimes called eSATA/USB) connector adds power to an external SATA connection, so that an additional power supply is not needed.[21]

Older desktop computers without a built-in eSATA interface can install an eSATA host bus adapter (HBA); if the motherboard supports SATA, an externally available eSATA connector can be added. Notebook computers can be upgraded with Cardbus[22] or ExpressCard[23] versions of an eSATA HBA. With passive adapters, the maximum cable length is reduced to due to the absence of compliant eSATA signal-levels.

eSATAp

eSATAp stands for powered eSATA. It is also known as Power over eSATA, Power eSATA, eSATA/USB Combo, or eSATA USB Hybrid Port (EUHP). An eSATAp port combines the 4 pins of the USB 2.0 (or earlier) port, the 7 pins of the eSATA port, and optionally two 12-volt power pins.[24] Both SATA traffic and device power are integrated in a single cable, as is the case with USB but not eSATA. Power at 5 volts is provided through two USB pins; power at 12 Volts may optionally be provided. Typically desktop, but not notebook, computers provide 12 volt power, so can power devices requiring this voltage, typically 3.5" disk and CD/DVD drives, in addition to 5 volt devices such as 2.5" drives.

Both USB and eSATA devices can be used with an eSATAp port, when plugged in with a USB or eSATA cable, respectively. An eSATA device cannot be powered via an eSATAp cable, but cables are available which make available both SATA or eSATA and power connectors from an eSATAp port.

An eSATAp connector can be built into a computer with internal SATA and USB, by fitting a bracket with connections for internal SATA, USB, and power connectors and an externally accessible eSATAp port.

Although eSATAp connectors have been built into several devices, manufacturers do not refer to an official standard.

Pre-standard implementations

  • Prior to the final eSATA 3 Gbit/s specification, a number of products were designed for external connection 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 could 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.
  • Prior to the final eSATA 6 Gbit/s specification many add-on cards and some motherboards advertised eSATA 6 Gbit/s support because they had 6 Gbit/s SATA 3.0 controllers for internal-only solutions. Those implementations are non-standard, and eSATA 6 Gbit/s requirements were ratified in the July 18, 2011 SATA 3.1 specification.[25] Some products might not be fully eSATA 6 Gbit/s compliant.

mSATA

An mSATA SSD on top of a 2.5 inch S-ATA
An mSATA SSD on top of a 2.5 inch S-ATA

Mini-SATA, which is distinct from the micro connector, was announced by the Serial ATA International Organization on September 21, 2009.[26] Applications include netbooks and other devices that require a smaller solid-state drive. The connector is similar in appearance to a PCI Express Mini Card interface,[27] and is electrically compatible, However the data signals (TX /RX SATA, PETn0 PETp0 PERn0 PERp0 PCI-express) need connection to the SATA host controller instead of the PCI-express host controller. Due to the absence of a standard for quite some time, there is still some confusion around this subject. For host devices which support either an mSATA SSD or mini-PCIe card interchangeably, this application note from NXP explains how to use a PCI-express/S-ATA router chip. This chip is essentially a four-channel bi-directional multiplexer. The vast majority of computer motherboards however have single-purpose headers which may support one of either an mSATA SSD or mini-PCIe card, but not both interchangeably.

Protocol

The SATA specification defines three distinct protocol layers: physical, link, and transport.

Physical layer

The physical layer defines SATA's electrical and physical characteristics (such as cable dimensions and parasitics, driver voltage level and receiver operating range), as well as the physical coding subsystem (bit-level encoding, device detection on the wire, and link initialization).

Physical transmission uses differential signaling. The SATA PHY contains a transmit pair and receive pair. When the SATA-link is not in use (example: no device attached), the transmitter allows the transmit pins to float to their common-mode voltage level. When the SATA-link is either active or in the link-initialization phase, the transmitter drives the transmit pins at the specified differential voltage (1.5v in SATA/I.)

SATA physical coding uses a line encoding system known as 8b/10b encoding. This scheme serves multiple functions required to sustain a differential serial link. First, the stream contains necessary synchronization information that allows for SATA host/drive to extract clocking. The 8b/10b encoded sequence embeds periodic edge transitions to allow the receiver to achieve bit-alignment without the use of a separately transmitted reference clock waveform. The sequence also maintains a neutral (DC-balanced) bitstream, which allows the transmit drivers and receiver inputs to be AC-coupled.

Also, Serial/ATA uses some of the of special characters defined in 8b/10b. In particular, the PHY layer uses the comma (K28.5) character to maintain symbol-alignment. A specific 4-symbol sequence, the ALIGN primitive, is used for clock rate-matching between the two devices on the link. Other special symbols communicate flow control information produced and consumed in the higher layers (link and transport.)

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

The PHY layer is responsible for detecting the other SATA/device on a cable, and link initialization. During the link-initialization process, the PHY is responsible for locally generating special out-of-band signals by switching the transmitter between electrical-idle and specific 10b-characters in a defined pattern, negotiating a mutually supported signalling rate (1.5, 3.0, or 6.0 Gbit/s), and finally synchronizing to the far-end device's PHY-layer data stream. During this time, no data is sent from the link-layer.

Once link-initialization has completed, the link-layer takes over data-transmission, with the PHY providing only the 8b/10b conversion before bit transmission.

Link layer

After the PHY-layer has established a link, the link layer is responsible for transmission and reception of FISs over the SATA link. FISs are packets containing control information or payload data. Each packet contains a header (identifying its type), and payload whose contents are dependent on the type. The link layer also manages flow control over the link.

Transport layer

The Transport layer controls the read and write operation (Frame Information Structure [FIS]) types. It is also implemented from programmable logic gates.

Topology

SATA topology: host (H), expansor (M), and device (D).
SATA topology: host (H), expansor (M), and device (D).

SATA uses a point-to-point architecture. The physical connection between a controller and a storage device is not shared among other controllers and storage devices. SATA defines multipliers, which allows a single SATA controller to drive multiple storage devices. The multiplier performs the function of a hub; the controller and each storage device is connected to the hub.

PC systems have SATA controllers built into the motherboard, typically featuring 2 to 6 ports. Additional ports can be installed through add-in SATA host adapters (available in variety of bus-interfaces: USB, PCI, PCI-e.)

Backward and forward compatibility

SATA and PATA

At the device level, SATA and PATA (Parallel AT 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.[28] 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, in general, disables some of the boards' PATA or SATA ports, since the standard PATA controller interface supports only 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."[29] 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 that 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. To prevent interoperability problems that could occur when next generation SATA drives are installed on motherboards with legacy standard SATA 1.5 Gbit/s motherboard host controllers, many manufacturers have made it easy to switch those newer drives to the previous standard's mode. For example, Seagate/Maxtor has added a user-accessible jumper-switch, known as the Force 150, to enable the drive to be switched between 1.5 Gbit/s and 3 Gbit/s operation. Western Digital uses a jumper setting called OPT1 Enabled to force 1.5 Gbit/s data transfer speed (OPT1 is enabled by putting the jumper on pins 5 & 6). Samsung drives can be switched to 1.5 Gbit/s mode using software that may be downloaded from the manufacturer's website. Upgrading a Samsung drive in this manner requires the temporary use of a SATA-2 (SATA 3.0 Gbit/s) controller while programming the drive.

The Force 150 switch is also useful when attaching SATA 300 hard drives on SATA controllers on PCI cards, since many of these controllers (such as the Silicon Images chips) will run at SATA300 even though the PCI bus cannot even reach SATA150 speeds. This can cause data corruption in operating systems that do not specifically test for this condition and limit the disk transfer speed.

SATA 3 Gbit/s and SATA 6 Gbit/s

Comparison to other interfaces

SATA and SCSI

Parallel SCSI uses a more complex bus than SATA, usually resulting in higher manufacturing costs. SCSI buses also allow connection of several drives on one shared channel, whereas SATA allows one drive per channel, unless using a port multiplier. Serial Attached SCSI uses the same physical interconnects as SATA, and most SAS HBAs also support SATA devices.

SATA 3 Gbit/s theoretically offers a maximum bandwidth of 300 MB/s per device which is only slightly worse than the rated speed for SCSI Ultra 320 with a maximum of 320 MB/s in total for all devices on a bus.[30] SCSI drives provide greater sustained throughput than multiple SATA drives connected via a simple (i.e. command-based) port multiplier because of disconnect-reconnect and aggregating performance.[31] In general, SATA devices link compatibly to SAS enclosures and adapters, whereas SCSI devices cannot be directly connected to a SATA bus.

SCSI, SAS, and fibre-channel (FC) drives are more expensive than SATA, so they are used in servers and disk arrays where the better performance justifies the additional cost. 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, in general, the failure rate of a disk drive is related to the quality of its heads, platters and supporting manufacturing processes, not to its interface.

Use of serial ATA in the business market increased from 22% in 2006 to 28% in 2008.

Comparison with 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) 1 (15 with port multiplier)
eSATAp [32]
SATA revision 3.0 6,000 600[33] 1 rowspan=3
SATA revision 2.0 3,000 300
SATA revision 1.0 1,500 150[34] 1 per line
PATA 133 1,064 133.5 0.46 (18 in) 2
SAS 600 6,000 600 10 rowspan=3 1 (>65k with expanders)
SAS 300 3,000 300
SAS 150 1,500 150
IEEE 1394 3200 3,144 393 100 (more with special cables) rowspan=3 63 (with hub)
IEEE 1394 800 786 98.25 100[35]
IEEE 1394 400 393 49.13 4.5[35][36]
USB 3.0* 5,000 400[37] 3[38] 127 (with hub)[38]
USB 2.0 480 60 5[39]
USB 1.0 12 1.5 3
SCSI Ultra-640 5,120 640 12 rowspan=2 15 (plus the HBA)
SCSI Ultra-320 2,560 320
Fibre Channel
over optic fibre
10,520 1,000 2 50,000 rowspan=2 126
(16,777,216 with switches)
Fibre Channel
over copper cable
4,000 400 12
InfiniBand
Quad Rate
10,000 1,000 5 (copper)[40][41] <10,000 (fiber) 1 with point to point
Many with switched fabric
Thunderbolt 10,000 1,250 3 (copper) 7
* 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 levels. 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.[42]

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.

See also

Notes and references

External links

ar: bs:SATA ca:Serial ATA cs:SATA de:Serial ATA et:SATA el:SATA es:Serial ATA eo:Serial ATA fa: fr:Serial ATA gl:Serial ATA ko:SATA hi: hr:Serial ATA id:Serial ATA it:Serial ATA he:Serial ATA lt:Serial ATA lmo:Serial ATA hu:Serial ATA ml: nl:Serial ATA ja: ATA no:Serial ATA pms:ESata pl:Serial ATA pt:Serial ATA ro:Serial ATA ru:SATA simple:Serial ATA sk:Serial ATA sr: fi:Serial ATA sv:Serial ATA tr:SATA uk:Serial ATA ur: zh:SATA






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