(SATA or Serial Advanced Technology Attachment) is a computer businterface 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 ATA (AT Attachment) standard (also known as EIDE), offering several advantages over the olderparallel ATA (PATA) interface: reduced cable-bulk and cost (7 conductors versus 40), nativehot 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.
As of 2009, SATA has replaced parallel ATA in most shipping consumer PC and laptopcomputers, and is expected to eventually replace PATA in embedded applications where space and cost are a consideration. 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.[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 T13subcommittee ATA, the INCITS T10 subcommittee (SCSI); a subgroup of T10 responsible for SAS. The complete specification from SATA-IO.[4] The remainder of this article will try to use the terminology and specifications of SATA-IO.[edit]SATA specification bodies
The SATA-IO succeeded in its mission of improving PATA. More than 1.1 billion SATA disk drives have been shipped from 2001 through 2008.[clarification needed] SATA’s market share in the desktop PC market is 99% in 2008. http://www.serialata.org/documents/SATA-Rev-30-Presentation.pdf
[edit]Features
[edit]Hotplug
The Serial ATA Spec includes logic for SATA device hotplugging. Devices and motherboards that meet the interoperability spec are capable of hot plugging.
[edit]Advanced Host Controller Interface
As their standard interface, SATA controllers use the AHCI (Advanced Host Controller Interface), allowing advanced features of SATA such as hotplug and native command queuing (NCQ). If AHCI is not enabled by the motherboard and chipset, SATA controllers typically operate in "IDE emulation" mode, which does not allow features of devices to be accessed if the ATA/IDE standard does not support them.
Windows device drivers that are labeled as SATA are 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, FreeBSD, Linux with version 2.6.19 onward,[5]as well as Solaris and OpenSolaris include support for AHCI, but older OSes 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]
[edit]Revisions
[edit]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. Taking 8b/10b encodingoverhead 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.[citation needed] 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.[citation needed]
As of April 2010 mechanical hard disk drives can transfer data at 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.
[edit]SATA Revision 2.0 (SATA 3 Gbit/s)
Second generation SATA interfaces running at 3.0 Gbit/s are shipping in high volume as of 2010, and prevalent in all[citation needed] SATA disk drives and the majority of 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 PATA/133. In addition, SATA devices offer enhancements such as NCQ that improve performance in a multitasking environment.
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 SATA 3 Gbit/s transfer rate, and this is being addressed with the SATA 6 Gbit/s interoperability standard.
[edit]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 (peak throughput about 600 MB/s (10b/8b coding plus 8 bit to one byte, without the protocol, or encoding overhead) was released on May 27, 2009.[10] While even the fastest conventional hard disk drives can barely saturate the original SATA 1.5 Gbit/s bandwidth, Solid-State Drives have already saturated the SATA 3 Gbit/s limit at 285 MB/s net read speed and 250 MB/s net write speed with the Sandforce 1200 and 1500 controller. However SandForce SSD controllers scheduled for release in 2011 have delivered 500 MB/s read/write rates,[11] and ten channels of fast flash can reach well over 500 MB/s with new ONFI drives – a move from SATA 3 Gbit/s to SATA 6 Gbit/s allows such devices to work at their full speed. As for standard hard disks, the reads from their built-in DRAM cache will end up faster across the new interface.[12] SATA 6 Gbit/s hard drives and motherboards are now shipping from several suppliers.
The new specification contains the following changes:
- 6 Gbit/s for scalable performance when used with SSDs
- 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 a meter. The new speeds may require higher power consumption for supporting chips, factors that new process technologies and power management techniques are expected to mitigate. The new specification can use existing SATA cables and connectors, although some OEMs are expected to upgrade host connectors for the higher speeds.[13] Also, the new standard is backwards compatible with SATA 3 Gbit/s.[14]
[edit]eSATA
Standardized in 2004, eSATA (e=external) provides a variant of SATA meant for external connectivity. It has revised electrical requirements in addition to incompatible cables and connectors:
- Minimum transmit potential increased: Range is 500–600 mV instead of 400–600 mV.
- Minimum receive potential decreased: Range is 240–600 mV instead of 325–600 mV.
- Identical protocol and logical signaling (link/transport-layer and above), allowing native SATA devices to be deployed in external enclosures with minimal modification
- Maximum cable length of 2 metres (6.6 ft) (USB and FireWire allow longer distances.)
- The external cable connector equates to a shielded version of the connector specified in SATA 1.0a with these basic differences:
- The external connector has no "L"-shaped key, and the guide features are vertically offset and reduced in size. This prevents the use of unshielded internal cables in external applications and vice-versa.
- To prevent ESD damage, the design increased insertion depth from 5 mm to 6.6 mm and the contacts are mounted farther back in both the receptacle and plug.
- To provide EMI protection and meet FCC and CE emission requirements, the cable has an extra layer of shielding, and the connectors have metal contact-points.
- The connector shield has springs as retention features built in on both the top and bottom surfaces.
- The external connector and cable have a design-life of over five thousand insertions and removals, whereas the internal connector is specified to withstand only fifty.
Aimed at the consumer market, eSATA enters an external storage market already served by the USB and FireWire interfaces. Most external hard-disk-drive cases with FireWire or USB interfaces use either PATA or SATA drives and "bridges" to translate between the drives' interfaces and the enclosures' external ports, and this bridging incurs some inefficiency. Some single disks can transfer 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, though the S3200 FireWire 1394b spec reaches ~400 MB/s (3.2 Gbit/s). Finally, some low-level drive features, such as S.M.A.R.T., may not operate through some USB [2] 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, even SATA drives will not have low-level features accessible. USB 3.0's 4.8 Gbit/s and Firewire's future 6.4 Gb/s (768 MB/s) will be faster than eSATA I, but the eSATA version of SATA 6G will operate at 6.0 Gb/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 at negligible differences of each other.[15]
eSATA can be differentiated from USB 2.0 and FireWire external storage for several reasons. As of early 2008, the vast majority of mass-market computers have USB ports and many computers and consumer electronic appliances have FireWire ports, but few devices have external SATA connectors. For small form-factor devices (such as external 2.5-inch (64 mm) disks), a PC-hosted USB or FireWire link supplies sufficient power to operate the device. Where a PC-hosted port is concerned, eSATA connectors cannot supply power, and would therefore be more cumbersome to use. Note that this problem has been solved by the introduction of eSATAp.[16] Some e-sata ports double as eSATA/USB.
Owners of desktop computers that lack a built-in eSATA interface can upgrade them with the installation of an eSATA host bus adapter(HBA), while notebooks can be upgraded with Cardbus[17] or ExpressCard[18] versions of an eSATA HBA. With passive adapters, the maximum cable length is reduced to 1 metre (3.3 ft) due to the absence of compliant eSATA signal-levels.
[edit]eSATAp
Main article: eSATAp
eSATAp is also known as Power over eSATA or eSATA/USB Combo. eSATAp port combines the strength of both eSATA (high speed) and USB (compatibility) into a single port. eSATAp devices are now capable of being self powered. On a desktop workstation, eSATAp port can supply 12 V to power up a 3.5" hard disk drive (HDD) or a 5.25" DVD-RW without needing separate power source as compared to eSATA and USB 2.0. On a notebook eSATAp port can supply 5 V to power up a 2.5" HDD/SSD as compared to eSATA. Many notebooks are now equipped with this combo port.
eSATAp can be implemented in all machines with a spare SATA port. These machines include PC notebooks, desktops, Apple Mac Pro, and Linux or Unix servers. This makes eSATAp an easy, economical, cross platform solution for external storage.
[edit]Pre-standard implementations
- Prior to the final eSATA 3 Gbit/s specification, a number of products existed designed for external connections of SATA drives. Some of these use the internal SATA connector or even connectors designed for other interface specifications, such as FireWire. These products are not eSATA compliant. The final eSATA specification features a specific connector designed for rough handling, similar to the regular SATA connector, but with reinforcements in both the male and female sides, inspired by the USB connector. eSATA resists inadvertent unplugging, and can withstand yanking or wiggling, which 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.[citation needed]
- Prior to the final eSATA 6 Gbit/s specification many add-on cards and some motherboards advertise eSATA 6 Gbit/s support because they have 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.[19] These products might not be eSATA 6 Gbit/s compliant.
[edit]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.[20]
[edit]Cables, connectors, and ports
Connectors and cables present the most visible differences between SATA and parallel ATA drives. Unlike PATA, the same connectors are used on 3.5-inch (89 mm) SATA hard disks for desktop and server computers and 2.5-inch (64 mm) disks for portable or small computers; this allows 2.5-inch (64 mm) drives to be used in desktop computers with only a mounting bracket and no wiring adapter. Smaller disks may use the mini-SATA spec, suitable for small-form-factor Serial ATA drives and mini SSDs.[21]
There is a special connector (eSATA) specified for external devices, and an optionally implemented provision for clips to hold internal connectors firmly in place. SATA drives may be plugged into SAS controllers and communicate on the same physical cable as native SAS disks, but SATA controllers cannot handle SAS disks.
There are female SATA ports (on motherboards for example) for use with SATA data cable with locks or clips, thus reducing the chance of accidentally unplugging while the machine is turned on -- As do SATA power/data connectors on optical and high density devices. Moreover, some SATA cables have orthogonally positioned heads in the shape of an 'L' which in effect ease the connection of devices to circuit boards.
[edit]Data
| Pin # | Function |
|---|---|
| 1 | Ground |
| 2 | A+ (transmit) |
| 3 | A− (transmit) |
| 4 | Ground |
| 5 | B− (receive) |
| 6 | B+ (receive) |
| 7 | Ground |
| 8 | Coding notch |
 | |
| A 7-pin Serial ATA right-angle data cable. | |
The SATA standard defines a data cable with seven conductors (3 grounds and 4 active data lines in two pairs) and 8 mm wide wafer connectors on each end. SATA cables can have lengths up to 1 metre (3.3 ft), and connect one motherboard socket to one hard drive. PATA ribbon cables, in comparison, connect one motherboard socket to one or two hard drives, carry either 40 or 80 wires, and are limited to 45 centimetres (18 in) in length by the PATA specification (however, cables up to 90 centimetres (35 in) are readily available). Thus, SATA connectors and cables are easier to fit in closed spaces, and reduce obstructions to air cooling. They are more susceptible to accidental unplugging and breakage than PATA, but cables can be purchased that have a locking feature, whereby a small (usually metal) spring holds the plug in the socket.
One of the problems associated with the transmission of data at high speed over electrical connections is 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. Some PATA cables use 80 wires, where only 40 wires carry signals.
[edit]Power Connectors
[edit]Standard connector
| Pin # | Mating | Function | |
|---|---|---|---|
| — | Coding notch | ||
| 1 | 3rd | 3.3 V | |
| 2 | 3rd | ||
| 3 | 2nd | ||
| 4 | 1st | Ground | |
| 5 | 2nd | ||
| 6 | 2nd | ||
| 7 | 2nd | 5 V | |
| 8 | 3rd | ||
| 9 | 3rd | ||
| 10 | 2nd | Ground | |
| 11 | 3rd | Staggered spinup/activity (in supporting drives) | |
| 12 | 1st | Ground | |
| 13 | 2nd | 12 V | |
| 14 | 3rd | ||
| 15 | 3rd | ||
 | |||
| A 15-pin Serial ATA power receptacle. This connector does not provide the extended pins 4 and 12 needed for hot-plugging.[22] | |||
The SATA standard specifies a power connector that differs from the decades-old four-pinMolex connector found on pre-SATA devices. Like the data cable, it is wafer-based, but its wider 15-pin shape prevents accidental mis-identification and forced insertion of the wrong connector type. Native SATA devices favor the SATA power-connector, although some early SATA drives retained older 4-pin Molex in addition to the SATA power connector.
SATA features more pins than the traditional connector for several reasons:
- A third voltage is supplied, 3.3 V, in addition to the traditional 5 V and 12 V.
- Each voltage 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 grouped together provide ground.
- For each of the three voltages, one of the three pins serves for hotplugging. The ground pins and power pins 3, 7, and 13 are longer on the plug (located on the SATA device) so they will connect first. A special hot-plug receptacle (on the cable or a backplane) can connect ground pins 4 and 12 first.
- Pin 11 can function for staggered spinup, activity indication, or nothing. Staggered spinup is used to prevent many drives from spinning up simultaneously, as this may draw too much power. Activity is an indication of whether the drive is busy, and is intended to give feedback to the user through an LED.
Adapters that can convert a 4-pin Molex connector to a SATA power connector exist. However, because the 4-pin Molex connectors do not provide 3.3 V power, these adapters provide only 5 V and 12 V power and leave the 3.3 V lines unconnected. This precludes the use of such adapters with drives that require 3.3 V power. Some 4-pin Molex to SATA power connectors have electronics included in the connector to also provide the 3.3 V power. Understanding this, drive manufacturers have largely left the 3.3 V power lines unused.
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