Serial ATA
Encyclopedia
Serial ATA 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 most shipping consumer desktop and laptop computer
s, and is expected to eventually replace PATA in embedded applications where space and cost are important factors. SATA's market share in the desktop PC market was 99% in 2008. PATA remains widely used in industrial and embedded applications that use CompactFlash
storage, though even here, the next CFast storage standard will be based on SATA.
T13subcommittee ATA, the INCITS T10 subcommittee (SCSI
); a subgroup of T10 responsible for Serial Attached SCSI
(SAS). The complete specification from SATA-IO. The remainder of this article will try to use the terminology and specifications of SATA-IO.
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, 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.
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, which is beyond the capabilities of the older PATA/133 specification and also exceeds a SATA 1.5 Gbit/s link.
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 are approaching the SATA 3 Gbit/s transfer rate; this is addressed with the SATA 6 Gbit/s interoperability standard.
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. It provides peak throughput of about 600 MB/s (Megabytes per second) including the protocol overhead (10b/8b coding with 8 bits to one byte). Solid-state drives have already saturated SATA 3 Gbit/s with 285/275 MB/s max read/write speed and 250 MB/s sustained with the Sandforce 1200 and 1500 controller. SandForce
SSD controllers released in 2011 have delivered 500 MB/s read/write rates, and ten channels of fast flash can reach well over 500 MB/s with ONFI
drives – a move from SATA 3 Gbit/s to SATA 6 Gbit/s allows such devices to work at their full speed. Full performance from Crucial's C300 SSD similarly require SATA 3.0. Standard hard disks cannot transfer data fast enough to require more than 3 Gbit/s; but they can nevertheless benefit from the later standard as reads from their built-in DRAM cache
will be faster across the later interface. According to Seagate "Cache-efficient desktop applications such as gaming, graphics design and digital video editing can experience immediate incremental performance using a SATA 6Gb/s interface". Drives with bigger, faster caches were introduced to benefit from the faster interface.
The 3.0 specification contains the following changes:
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 OEM
s were expected to upgrade host connectors for the higher speeds.
The later standard is backwards compatible with SATA 3 Gbit/s.
In order to provide the industry with consistent terminology, the SATA-IO has compiled a set of marketing guidelines for the third revision of the specification.
Using the terms SATA III or SATA 3.0 to refer to a SATA 6 Gbit/s product is unclear and not preferred. SATA-IO has provided a guideline to foster consistent marketing terminology across the industry.
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.
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 are used, on motherboards for example, for use with SATA data cables with 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.
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 metres (3.3 ft), and connect one motherboard socket to one hard drive. PATA ribbon cable
s, in comparison, connect one motherboard socket to one or two hard drives, carry either 40 or 80 wires, and are limited to 45 centimetres (17.7 in) in length by the PATA specification (however, cables up to 90 centimetres (35.4 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.
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 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:
Adapters are available that convert a 4-pin Molex connector
to a SATA power connector. Generally, because the power lines on 4-pin Molex connectors do not provide 3.3 V power, these adapters provide only 5 V and 12 V power on the SATA end and leave the 3.3 V lines unconnected. This precludes the use of such adapters with drives that require 3.3 V power. Because of this, drive manufacturers have largely not used the 3.3 V power lines. There also exist some 4-pin Molex to SATA power adapters which include electronics to provide 3.3 V power.
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.
The micro connector originated with SATA 2.6. It is intended for 1.8 inches (45.7 mm) hard drives. There is also a micro data connector, similar in appearance to but slightly thinner than the standard data connector.
Standardized in 2004, eSATA (e standing for external) provides a variant of SATA meant for external connectivity. While it has revised electrical requirements and the connectors and cables are not identical with SATA, the protocol and logical signaling are compatible on the (internal) SATA level:
Aimed at the consumer market, eSATA enters an external storage market served also 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; this bridging incurs some inefficiency. Some single disks can transfer 157 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. 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 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. Once an interface can transfer data as fast as a drive can handle them, increasing the interface speed does not improve data transfer.
Most 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 inches (63.5 mm) 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.
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 or ExpressCard
versions of an eSATA HBA. With passive adapters, the maximum cable length is reduced to 1 metres (3.3 ft) due to the absence of compliant eSATA signal-levels.
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 eSATA 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.
s and other devices that require a smaller solid-state drive
. The connector is similar in appearance to a PCI Express Mini Card interface, but is electrically incompatible.
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.
, 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.)
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 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.
with future revisions of the SATA standard.
According to the hard drive manufacturer Maxtor, motherboard host controllers using the VIA and SIS chipsets VT8237, VT8237R, VT6420, VT6421L, SIS760, SIS964 found on the ECS 755-A2 manufactured in 2003, do not support SATA 3 Gbit/s drives. Additionally, these host controllers do not support optical disc drives that support only the SATA 3 Gbit/s standard. Users with a SATA 1.5 Gbit/s motherboard with one of the listed chipsets should either buy an ordinary SATA 1.5 Gbit/s hard disk, buy a SATA 3 Gbit/s hard disk switchable to 1.5 Gbit/s, or buy a PCI or PCI-E card to add full SATA 3 Gbit/s capability and compatibility.
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.
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.
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 with a maximum of 320 MB/s in total for all devices on a bus. 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. 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 server
s and disk array
s 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.
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 adapter
s 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.
s are tools which collect, analyze, decode, and store rapidly changing signals and waveforms, which can then be studied.
Computer bus
In computer architecture, a bus is a subsystem that transfers data between components inside a computer, or between computers.Early computer buses were literally parallel electrical wires with multiple connections, but the term is now used for any physical arrangement that provides the same...
interface for connecting host bus adapters
Host adapter
In computer hardware, a host controller, host adapter, or host bus adapter connects a host system to other network and storage devices...
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
Hot swapping
Hot swapping and hot plugging are terms used to describe the functions of replacing computer system components without shutting down the system...
, 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
Serial communications
In telecommunication and computer science, serial communication is the process of sending data one bit at a time, sequentially, over a communication channel or computer bus. This is in contrast to parallel communication, where several bits are sent as a whole, on a link with several parallel channels...
cable over two pairs of conductors. In contrast, parallel ATA (the redesignation
Retronym
A retronym is a type of neologism that provides a new name for an object or concept to differentiate the original form or version of it from a more recent form or version. The original name is most often augmented with an adjective to account for later developments of the object or concept itself...
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 most shipping consumer desktop and laptop computer
Computer
A computer is a programmable machine designed to sequentially and automatically carry out a sequence of arithmetic or logical operations. The particular sequence of operations can be changed readily, allowing the computer to solve more than one kind of problem...
s, and is expected to eventually replace PATA in embedded applications where space and cost are important factors. SATA's market share in the desktop PC market was 99% in 2008. PATA remains widely used in industrial and embedded applications that use CompactFlash
CompactFlash
CompactFlash is a mass storage device format used in portable electronic devices. Most CompactFlash devices contain flash memory in a standardized enclosure. The format was first specified and produced by SanDisk in 1994...
storage, though even here, the next CFast storage standard will be based on SATA.
Specification bodies
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 INCITSINCITS
The InterNational Committee for Information Technology Standards, or INCITS , is an ANSI-accredited forum of IT developers. It was formerly known as the X3 and NCITS....
T13subcommittee ATA, the INCITS T10 subcommittee (SCSI
SCSI
Small Computer System Interface is a set of standards for physically connecting and transferring data between computers and peripheral devices. The SCSI standards define commands, protocols, and electrical and optical interfaces. SCSI is most commonly used for hard disks and tape drives, but it...
); a subgroup of T10 responsible for Serial Attached SCSI
Serial Attached SCSI
Serial Attached SCSI is a computer bus used to move data to and from computer storage devices such as hard drives and tape drives. SAS depends on a point-to-point serial protocol that replaces the parallel SCSI bus technology that first appeared in the mid 1980s in data centers and workstations,...
(SAS). The complete specification from SATA-IO. The remainder of this article will try to use the terminology and specifications of SATA-IO.
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)Advanced Host Controller Interface
The Advanced Host Controller Interface is a technical standard defined by Intel that specifies the operation of Serial ATA host bus adapters in a non-implementation-specific manner....
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
Native Command Queuing
Native Command Queuing is a technology designed to increase performance of SATA hard disks under certain conditions by allowing the individual hard disk to internally optimize the order in which received read and write commands are executed...
(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
RAID
RAID is a storage technology that combines multiple disk drive components into a logical unit...
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
Microsoft Windows
Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...
, Mac OS X
Mac OS X
Mac OS X is a series of Unix-based operating systems and graphical user interfaces developed, marketed, and sold by Apple Inc. Since 2002, has been included with all new Macintosh computer systems...
, FreeBSD
FreeBSD
FreeBSD is a free Unix-like operating system descended from AT&T UNIX via BSD UNIX. Although for legal reasons FreeBSD cannot be called “UNIX”, as the direct descendant of BSD UNIX , FreeBSD’s internals and system APIs are UNIX-compliant...
, Linux
Linux kernel
The Linux kernel is an operating system kernel used by the Linux family of Unix-like operating systems. It is one of the most prominent examples of free and open source software....
with version 2.6.19 onward, as well as Solaris and OpenSolaris
OpenSolaris
OpenSolaris was an open source computer operating system based on Solaris created by Sun Microsystems. It was also the name of the project initiated by Sun to build a developer and user community around the software...
, include support for AHCI, but older OSs such as Windows XP
Windows XP
Windows XP is an operating system produced by Microsoft for use on personal computers, including home and business desktops, laptops and media centers. First released to computer manufacturers on August 24, 2001, it is the second most popular version of Windows, based on installed user base...
do not. Even in those instances, a proprietary driver may have been created for a specific chipset, such as Intel's.
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 encoding8B/10B encoding
In telecommunications, 8b/10b is a line code that maps 8-bit symbols to 10-bit symbols to achieve DC-balance and bounded disparity, and yet provide enough state changes to allow reasonable clock recovery. This means that the difference between the count of 1s and 0s in a string of at least 20 bits...
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
AT Attachment
Parallel ATA , originally ATA, is an interface standard for the connection of storage devices such as hard disks, solid-state drives, floppy drives, and optical disc drives in computers. The standard is maintained by X3/INCITS committee...
/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, 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 encoding8B/10B encoding
In telecommunications, 8b/10b is a line code that maps 8-bit symbols to 10-bit symbols to achieve DC-balance and bounded disparity, and yet provide enough state changes to allow reasonable clock recovery. This means that the difference between the count of 1s and 0s in a string of at least 20 bits...
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 are approaching 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 OrganizationSerial ATA International Organization
Serial ATA International Organization is an independent, non-profit organization which provides the computing industry with guidance and support for implementing the SATA specification. SATA-IO was developed by and for leading industry companies...
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. It provides peak throughput of about 600 MB/s (Megabytes per second) including the protocol overhead (10b/8b coding with 8 bits to one byte). Solid-state drives have already saturated SATA 3 Gbit/s with 285/275 MB/s max read/write speed and 250 MB/s sustained with the Sandforce 1200 and 1500 controller. SandForce
SandForce
SandForce is an American "fabless" semiconductor company based in Milpitas, California, that designs and manufactures flash memory controllers for solid-state drives . On October 26th 2011 it was acquired by LSI Corporation....
SSD controllers released in 2011 have delivered 500 MB/s read/write rates, and ten channels of fast flash can reach well over 500 MB/s with ONFI
Open NAND Flash Interface Working Group
The Open NAND Flash Interface Working Group , is a consortium of technology companies working to develop open standards for NAND flash memory chips and devices that communicate with them...
drives – a move from SATA 3 Gbit/s to SATA 6 Gbit/s allows such devices to work at their full speed. Full performance from Crucial's C300 SSD similarly require SATA 3.0. Standard hard disks cannot transfer data fast enough to require more than 3 Gbit/s; but they can nevertheless benefit from the later standard as reads from their built-in DRAM cache
Disk buffer
In computer storage, disk buffer is the embedded memory in a hard drive acting as a buffer between the rest of the computer and the physical hard disk platter that is used for storage...
will be faster across the later interface. According to Seagate "Cache-efficient desktop applications such as gaming, graphics design and digital video editing can experience immediate incremental performance using a SATA 6Gb/s interface". Drives with bigger, faster caches were introduced to benefit from the faster interface.
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 QueuingNative Command QueuingNative Command Queuing is a technology designed to increase performance of SATA hard disks under certain conditions by allowing the individual hard disk to internally optimize the order in which received read and write commands are executed...
(NCQ) streaming command to enable isochronousIsochronousIsochronous : From Greek iso, equal + chronos, time. It literally means regularly, or at equal time intervals. In general English language, it refers to something that occurs at a regular interval, of the same duration; as opposed to synchronous which refers to more than one thing happening at the...
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 forceLow insertion forcethumb|300px|right|LIF-connector of a 1.8" [[hard disk drive]]Low-insertion-force sockets are integrated circuit sockets that are designed so the force required to insert or remove a package is low....
(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 OEM
Original Equipment Manufacturer
An original equipment manufacturer, or OEM, manufactures products or components that are purchased by a company and retailed under that purchasing company's brand name. OEM refers to the company that originally manufactured the product. When referring to automotive parts, OEM designates a...
s were expected to upgrade host connectors for the higher speeds.
The later standard is backwards compatible with SATA 3 Gbit/s.
SATA revision 3.1
New:- mSATA, SATA for solid-state drives in mobile computing devices, a PCI Express Mini Card-like connector which is electrically SATA
- Zero-power optical disk drive, idle SATA optical drive draws no power
- Queued TRIMTrimTrim may refer to:* Cutting small pieces off something** Book trimming, a stage of the publishing process** Editing*** Editing a posting style in online discourse** Pruning, trimming as a form of pruning often used on trees-Places:...
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 electronicsConsumer electronicsConsumer electronics are electronic equipment intended for everyday use, most often in entertainment, communications and office productivity. Radio broadcasting in the early 20th century brought the first major consumer product, the broadcast receiver...
devices
Terminology
The name SATA II has become synonymous with the 3 Gbit/s standard.In order to provide the industry with consistent terminology, the SATA-IO has compiled a set of marketing guidelines for the third revision of the specification.
- The SATA 6 Gbit/s specification should be called Serial ATA International Organization: Serial ATA Revision 3.0.
- The technology itself is to be referred to as SATA 6 Gb/s.
- A product using this standard should be called the SATA 6 Gb/s [product name].
Using the terms SATA III or SATA 3.0 to refer to a SATA 6 Gbit/s product is unclear and not preferred. SATA-IO has provided a guideline to foster consistent marketing terminology across the industry.
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 inches (88.9 mm) SATA hard disks for desktop and server computers and 2.5 inches (63.5 mm) disks for portable or small computers.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.
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 are used, on motherboards for example, for use with SATA data cables with 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 # | Function |
|---|---|
| 1 | Ground |
| 2 | A+ (transmit) |
| 3 | A− (transmit) |
| 4 | Ground |
| 5 | B− (receive) |
| 6 | B+ (receive) |
| 7 | Ground |
| — | Coding notch |
Ribbon cable
A ribbon cable is a cable with many conducting wires running parallel to each other on the same flat plane. As a result the cable is wide and flat. Its name comes from the resemblance of the cable to a piece of ribbon.Ribbon cables are usually seen for internal peripherals in computers, such as...
s, in comparison, connect one motherboard socket to one or two hard drives, carry either 40 or 80 wires, and are limited to 45 centimetres (17.7 in) in length by the PATA specification (however, cables up to 90 centimetres (35.4 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.
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
Differential signaling
Differential signaling is a method of transmitting information electrically by means of two complementary signals sent on two separate wires. The technique can be used for both analog signaling, as in some audio systems, and digital signaling, as in RS-422, RS-485, Ethernet , PCI Express and USB...
. This is an enhancement over PATA, which uses single-ended signaling.
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 | ||
Power connector
Power connector may refer to:* AC power plugs and sockets* Industrial power plug* DC connector* Blade connector, commonly found in cars for quick connection of wiring to electrical components* IEC 60309 , so-called "Commando" plug and socket...
that differs from the decades-old four-pin Molex connector
Molex connector
Molex connector is the vernacular term for a two-piece pin and socket interconnection, most frequently disk drive connectors. Pioneered by Molex Connector Company, the two-piece design became an early electronic standard. Molex developed and patented the first examples of this connector style in...
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 voltageVoltageVoltage, otherwise known as electrical potential difference or electric tension is the difference in electric potential between two points — or the difference in electric potential energy per unit charge between two points...
is supplied, 3.3 V, in addition to the traditional 5 V and 12 V. - 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.)
- Five pins provide ground.
- For each of the three voltages, one of the three pins serves for hotpluggingHot swappingHot swapping and hot plugging are terms used to describe the functions of replacing computer system components without shutting down the system...
. 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 collectorOpen collectorAn open collector is a common type of output found on many integrated circuits . Instead of outputting a signal of a specific voltage or current, the output signal is applied to the base of an internal NPN transistor whose collector is externalized on a pin of the IC. The emitter of the...
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 LEDLEdLEd is a TeX/LaTeX editing software working under Microsoft Windows. It is a freeware product....
.
Adapters are available that convert a 4-pin Molex connector
Molex connector
Molex connector is the vernacular term for a two-piece pin and socket interconnection, most frequently disk drive connectors. Pioneered by Molex Connector Company, the two-piece design became an early electronic standard. Molex developed and patented the first examples of this connector style in...
to a SATA power connector. Generally, because the power lines on 4-pin Molex connectors do not provide 3.3 V power, these adapters provide only 5 V and 12 V power on the SATA end and leave the 3.3 V lines unconnected. This precludes the use of such adapters with drives that require 3.3 V power. Because of this, drive manufacturers have largely not used the 3.3 V power lines. There also exist some 4-pin Molex to SATA power adapters which include electronics to provide 3.3 V power.
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 | ||
Micro connector
| Pin # | Mating (Backplane) | 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 | ||
The micro connector originated with SATA 2.6. It is intended for 1.8 inches (45.7 mm) hard drives. There is also a micro data connector, similar in appearance to but slightly thinner than the standard data connector.
eSATA
- 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 ESDElectrostatic dischargeElectrostatic discharge is a serious issue in solid state electronics, such as integrated circuits. Integrated circuits are made from semiconductor materials such as silicon and insulating materials such as silicon dioxide...
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 EMIElectromagnetic interferenceElectromagnetic interference is disturbance that affects an electrical circuit due to either electromagnetic induction or electromagnetic radiation emitted from an external source. The disturbance may interrupt, obstruct, or otherwise degrade or limit the effective performance of the circuit...
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 in 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. 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, 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
USB 3.0
USB 3.0 is the second major revision of the Universal Serial Bus standard for computer connectivity.USB 3.0 has transmission speeds of up to 5 Gbit/s, which is 10 times faster than USB 2.0 . USB 3.0 significantly reduces the time required for data transmission, reduces power consumption, and...
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 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
JMicron
JMicron Technology Corporation is a Taiwanese manufacturer of integrated circuits which mostly produces Serial ATA and related controller chips....
, and NVIDIA
NVIDIA
Nvidia is an American global technology company based in Santa Clara, California. Nvidia is best known for its graphics processors . Nvidia and chief rival AMD Graphics Techonologies have dominated the high performance GPU market, pushing other manufacturers to smaller, niche roles...
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. Once an interface can transfer data as fast as a drive can handle them, increasing the interface speed does not improve data transfer.
Most 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 inches (63.5 mm) 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
ESATAp
In computing, eSATAp is a high speed connection for external storage devices. It is a combination of serial port connectors into which an eSATAp, eSATA or USB devices can be plugged...
(but mechanically incompatible, sometimes called eSATA/USB) connector adds power to an external SATA connection, so that an additional power supply is not needed.
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 or ExpressCard
ExpressCard
ExpressCard is an interface to allow peripheral devices to be connected to a computer, usually a laptop computer. Formerly called NEWCARD, the ExpressCard standard specifies the design of slots built into the computer and of cards which can be inserted into ExpressCard slots. The cards contain...
versions of an eSATA HBA. With passive adapters, the maximum cable length is reduced to 1 metres (3.3 ft) due to the absence of compliant eSATA signal-levels.
eSATAp
eSATAp stands for powered eSATA. It is also known as Power over eSATA, eSATA USB Hybrid Port (EUHP), or eSATA/USB Combo. 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. 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 eSATA 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 will be ratified in the upcoming SATA 3.1 specification. These products might not be eSATA 6 Gbit/s compliant.
mSATA
Mini-SATA, which is distinct from the micro connector, was announced by the Serial ATA International Organization on September 21, 2009. Applications include netbookNetbook
Netbooks are a category of small, lightweight, legacy-free, and inexpensive laptop computers.At their inception in late 2007 as smaller notebooks optimized for low weight and low cost — netbooks omitted certain features , featured smaller screens and keyboards, and offered reduced computing...
s and other devices that require a smaller solid-state drive
Solid-state drive
A solid-state drive , sometimes called a solid-state disk or electronic disk, is a data storage device that uses solid-state memory to store persistent data with the intention of providing access in the same manner of a traditional block i/o hard disk drive...
. The connector is similar in appearance to a PCI Express Mini Card interface, but is electrically incompatible.
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
8B/10B encoding
In telecommunications, 8b/10b is a line code that maps 8-bit symbols to 10-bit symbols to achieve DC-balance and bounded disparity, and yet provide enough state changes to allow reasonable clock recovery. This means that the difference between the count of 1s and 0s in a string of at least 20 bits...
. 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
Low voltage differential signaling
Low-voltage differential signaling, or LVDS, is an electrical digital signaling system that can run at very high speeds over inexpensive twisted-pair copper cables. It was introduced in 1994, and has since become very popular in computers, where it forms part of very high-speed networks and...
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 between 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 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 multipliersPort multiplier
A Serial ATA port multiplier is a device that allows one to connect multiple SATA devices to a single SATA host port in a similar manner to that of a USB hub...
, 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.)
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. 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." 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
Peripheral Component Interconnect
Conventional PCI is a computer bus for attaching hardware devices in a computer...
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 compatibilityForward compatibility
Forward compatibility or upward compatibility is a compatibility concept for systems design, as e.g. backward compatibility. Forward compatibility aims at the ability of a design to gracefully accept input intended for later versions of itself...
with future revisions of the SATA standard.
According to the hard drive manufacturer Maxtor, motherboard host controllers using the VIA and SIS chipsets VT8237, VT8237R, VT6420, VT6421L, SIS760, SIS964 found on the ECS 755-A2 manufactured in 2003, do not support SATA 3 Gbit/s drives. Additionally, these host controllers do not support optical disc drives that support only the SATA 3 Gbit/s standard. Users with a SATA 1.5 Gbit/s motherboard with one of the listed chipsets should either buy an ordinary SATA 1.5 Gbit/s hard disk, buy a SATA 3 Gbit/s hard disk switchable to 1.5 Gbit/s, or buy a PCI or PCI-E card to add full SATA 3 Gbit/s capability and compatibility.
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 and SCSI
SCSISCSI
Small Computer System Interface is a set of standards for physically connecting and transferring data between computers and peripheral devices. The SCSI standards define commands, protocols, and electrical and optical interfaces. SCSI is most commonly used for hard disks and tape drives, but it...
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.
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 with a maximum of 320 MB/s in total for all devices on a bus. SCSI drives provide greater sustained throughput than multiple SATA drives connected via a simple (i.e. command-based) port multiplier
Port multiplier
A Serial ATA port multiplier is a device that allows one to connect multiple SATA devices to a single SATA host port in a similar manner to that of a USB hub...
because of disconnect-reconnect and aggregating performance. 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 server
Server (computing)
In the context of client-server architecture, a server is a computer program running to serve the requests of other programs, the "clients". Thus, the "server" performs some computational task on behalf of "clients"...
s and disk array
Disk array
A disk array is a disk storage system which contains multiple disk drives. It is differentiated from a disk enclosure, in that an array has cache memory and advanced functionality, like RAID and virtualization.Components of a typical disk array include:...
s where the better performance justifies the additional cost. Inexpensive ATA and SATA drives evolved in the home-computer
Home computer
Home computers were a class of microcomputers entering the market in 1977, and becoming increasingly common during the 1980s. They were marketed to consumers as affordable and accessible computers that, for the first time, were intended for the use of a single nontechnical user...
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 Port multiplier A Serial ATA port multiplier is a device that allows one to connect multiple SATA devices to a single SATA host port in a similar manner to that of a USB hub... ) |
|
| eSATAp ESATAp In computing, eSATAp is a high speed connection for external storage devices. It is a combination of serial port connectors into which an eSATAp, eSATA or USB devices can be plugged... |
|||||
| SATA revision 3.0 | 6,000 | 600 | 1 | rowspan=3 | |
| SATA revision 2.0 | 3,000 | 300 | |||
| SATA revision 1.0 | 1,500 | 150 | 1 per line | ||
| PATA 133 | 1,064 | 133.5 | 0.46 (18 in) | 2 | |
| SAS 600 Serial Attached SCSI Serial Attached SCSI is a computer bus used to move data to and from computer storage devices such as hard drives and tape drives. SAS depends on a point-to-point serial protocol that replaces the parallel SCSI bus technology that first appeared in the mid 1980s in data centers and workstations,... |
6,000 | 600 | 10 | rowspan=3 | 1 (>65k with expanders) |
| SAS 300 Serial Attached SCSI Serial Attached SCSI is a computer bus used to move data to and from computer storage devices such as hard drives and tape drives. SAS depends on a point-to-point serial protocol that replaces the parallel SCSI bus technology that first appeared in the mid 1980s in data centers and workstations,... |
3,000 | 300 | |||
| SAS 150 Serial Attached SCSI Serial Attached SCSI is a computer bus used to move data to and from computer storage devices such as hard drives and tape drives. SAS depends on a point-to-point serial protocol that replaces the parallel SCSI bus technology that first appeared in the mid 1980s in data centers and workstations,... |
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 | ||
| IEEE 1394 400 | 393 | 49.13 | 4.5 | ||
| USB Universal Serial Bus USB is an industry standard developed in the mid-1990s that defines the cables, connectors and protocols used in a bus for connection, communication and power supply between computers and electronic devices.... 3.0* |
5,000 | 400 | 3 | 127 (with hub) | |
| USB Universal Serial Bus USB is an industry standard developed in the mid-1990s that defines the cables, connectors and protocols used in a bus for connection, communication and power supply between computers and electronic devices.... 2.0 |
480 | 60 | 5 | ||
| USB Universal Serial Bus USB is an industry standard developed in the mid-1990s that defines the cables, connectors and protocols used in a bus for connection, communication and power supply between computers and electronic devices.... 1.0 |
12 | 1.5 | 3 | ||
| SCSI SCSI Small Computer System Interface is a set of standards for physically connecting and transferring data between computers and peripheral devices. The SCSI standards define commands, protocols, and electrical and optical interfaces. SCSI is most commonly used for hard disks and tape drives, but it... Ultra-640 |
5,120 | 640 | 12 | rowspan=2 | 15 (plus the HBA) |
| SCSI SCSI Small Computer System Interface is a set of standards for physically connecting and transferring data between computers and peripheral devices. The SCSI standards define commands, protocols, and electrical and optical interfaces. SCSI is most commonly used for hard disks and tape drives, but it... Ultra-320 |
2,560 | 320 | |||
| Fibre Channel Fibre Channel Fibre Channel, or FC, is a gigabit-speed network technology primarily used for storage networking. Fibre Channel is standardized in the T11 Technical Committee of the InterNational Committee for Information Technology Standards , an American National Standards Institute –accredited standards... over optic fibre |
10,520 | 1,000 | 2–50,000 | rowspan=2 | 126 (16,777,216 with switches) |
| Fibre Channel Fibre Channel Fibre Channel, or FC, is a gigabit-speed network technology primarily used for storage networking. Fibre Channel is standardized in the T11 Technical Committee of the InterNational Committee for Information Technology Standards , an American National Standards Institute –accredited standards... over copper cable |
4,000 | 400 | 12 | ||
| InfiniBand InfiniBand InfiniBand is a switched fabric communications link used in high-performance computing and enterprise data centers. Its features include high throughput, low latency, quality of service and failover, and it is designed to be scalable... Quad Rate |
10,000 | 1,000 | 5 (copper) <10,000 (fiber) |
1 with point to point Many with switched fabric Switched fabric Switched fabric, switching fabric, or just fabric, is a network topology where network nodes connect with each other via one or more network switches . The term is popular in telecommunication, Fibre Channel storage area networks and other high-speed networks, including InfiniBand... |
|
| Thunderbolt | 10,000 | 1,250 | 3 (copper) | 7 |
- * USBUniversal Serial BusUSB is an industry standard developed in the mid-1990s that defines the cables, connectors and protocols used in a bus for connection, communication and power supply between computers and electronic devices....
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 adapter
Host adapter
In computer hardware, a host controller, host adapter, or host bus adapter connects a host system to other network and storage devices...
s 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.
Development tools
In development of new products, or when troubleshooting the Serial ATA bus, examination of hardware signals can be very important to find problems. Logic analyzers and bus analyzerBus analyzer
A bus analyzer is a computer bus analysis tool, often a combination of hardware and software, used during development of hardware or device drivers for a specific bus, for diagnosing bus or device failures, or reverse engineering....
s are tools which collect, analyze, decode, and store rapidly changing signals and waveforms, which can then be studied.
See also
- libATALibATAlibATA is a library used inside the Linux kernel to support ATA host controllers and devices. libATA provides an ATA driver API, class transports for ATA and ATAPI devices, and SCSI/ATA translation for ATA devices according to the T10 SAT specification...
- List of device bit rates
- FATA (hard drive)
External links
- Serial ATA International Organization (SATA-IO)
- EETimes Serial ATA and the evolution in data storage technology, Mohamed A. Salem
- "SATA-1" specification, as a zipped pdf; Serial ATA: High Speed Serialized AT Attachment, Revision 1.0a, 7-January-2003.
- Errata and Engineering Change Notices to above "SATA-1" specification, as a zip of pdfs
- Dispelling the Confusion: SATA II does not mean 3 Gbit/s
- SATA motherboard connector pinout
- Serial ATA Connector Schematic and Pinout
- Serial ATA server and storage use cases
- How to Install and Troubleshoot SATA Hard Drives
- Serial ATA and the 7 Deadly Sins of Parallel ATA
- Everything You Need to Know About Serial ATA
- Barracuda XT - the first SATA 6Gb/s HDD
- Mini-FAQ on SATA II (specifications/performance/compatibility)
- USB 3.0 vs. eSATA: Is faster better?
- UniATA, the universal, free, open-source ATA driver with PATA/SATA support
- Adapter or converter for a SATA drive to become a PATA drive
