Serial ATA | |
First-generation (1.5 Gbit/s) SATA ports on a motherboard |
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Year created | 2003 |
---|---|
Supersedes | Parallel ATA (PATA) |
Capacity | 1.5, 3.0, 6.0 Gbit/s |
Style | Serial |
Hotplugging interface | Yes[1] |
External interface | Yes (eSATA) |
Serial ATA (SATA or Serial Advanced Technology Attachment) 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 ATA (AT Attachment) standard (also known as EIDE). It is able to use the same low level commands, but serial ATA host-adapters and devices communicate via a high-speed serial cable over two pairs of conductors. In contrast, the parallel ATA (the redesignation for the legacy ATA specifications) used 16 data conductors each operating at a much lower speed.
SATA offers several advantages over the older parallel ATA (PATA) interface: reduced cable-bulk and cost (reduced from 80 wires to seven), faster and more efficient data transfer, and hot swapping.
The SATA host adapter is integrated into almost all modern consumer laptop computers and desktop motherboards. As of 2009[update], SATA has replaced parallel ATA in most shipping consumer PCs. PATA remains in industrial and embedded applications dependent on CompactFlash storage although the new CFast storage standard will be based on SATA.[2][3]
Contents |
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.
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. SATA’s market share in the desktop PC market is 99% in 2008. http://www.serialata.org/documents/SATA-Rev-30-Presentation.pdf
The Serial ATA Spec, includes logic for SATA device hotplugging. Devices and motherboards that meet the interoperability spec are capable of hot plugging.
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]
First-generation SATA interfaces, now known as SATA 1.5 Gbit/s, communicate at a rate of 1.5 Gbit/s. Taking 8b/10b encoding overhead into account, they have an actual uncoded transfer rate of 1.2 Gbit/s (1500000000*8/10/1024/1024/8 ≅ 143.05 MiB/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 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. High-performance flash drives can transfer data at up to 308 MB/s which exceeds a SATA 3 Gbit/s link.[8]
Second generation SATA interfaces running at 3.0 Gbit/s are shipping in high volume as of 2010[update], and prevalent in all 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 (286 MiB/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 Gb/s interoperability standard.
Serial ATA International Organization presented the draft specification of SATA 6 Gbit/s physical layer in July 2008,[9] and ratified its physical layer specification on August 18, 2008.[10] 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.[11] 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 250 MB/s net read speed. Ten channels of fast flash can reach well over 500 MB/s with new ONFI drives, so a move from SATA 3 Gbit/s to SATA 6 Gbit/s would benefit the flash read speeds. As for the standard hard disks, the reads from their built-in DRAM cache will end up faster across the new interface.[12] SATA 6 Gbit/s hard drives and Motherboards are now shipping from several suppliers.
The new 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 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]
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:
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 Gb/s, which was colloquially referred to as "SATA 3G" [bps] or "SATA 300" [MB/s] since 1.5 Gb/s SATA I and 1.5 Gb/s SATA II were referred to as both "SATA 1.5G" [b/s] or "SATA 150" [MB/s]). 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 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. Full SATA speed for external disks (115 MB/s) have been measured with external RAID enclosures.
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. 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. A list of notebooks with this new port is available here [3]
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.
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.
Using the terms SATA III or SATA 3.0 to refer to a SATA 6 Gb/s product, is unclear and not preferred. SATA-IO has provided a guideline to foster consistent marketing terminology across the industry.[20]
Connectors and cables present the most visible differences between SATA and parallel ATA drives. Unlike PATA, the same connectors are used on 3.5-inch SATA hard disks for desktop and server computers and 2.5-inch disks for portable or small computers; this allows 2.5-inch drives to be used in desktop computers with only a mounting bracket and no wiring adapter. Smaller disks may use the mini-SATA spec, suitable for small-form-factor Serial ATA drives and mini SSDs.[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 SATA ports (on motherboards of a PC) that can use SATA data cable with locks or clips, thus reducing the chance of accidentally unplugging while the PC is turned on. So does the same with SATA power connector and SATA data connector connected to a SATA HDD or SATA optical drive. Also, there is a right-angled connector on one end of some SATA data cables, which can be used when connecting to a SATA HDD or SATA optical drive.
Pin # | Function |
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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 up to two hard drives, carry either 40 or 80 wires, and are limited to 45 centimetres (18 in) in length by the PATA specification (however, cables up to 90 centimetres (35 in) are readily available). Thus, SATA connectors and cables are easier to fit in closed spaces and reduce obstructions to air cooling. They are more susceptible to accidental unplugging and breakage than PATA, but cables can be purchased that have a locking feature, whereby a small (usually metal) spring holds the plug in the socket.
One of the problems associated with the transmission of data at high speed over electrical connections is loosely described as noise. Despite attempts to avoid it, some electrical coupling will exist both between data circuits and between them and other circuits. As a result, the data circuits can both affect other circuits, whether they are within the same piece of equipment or not, and 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.
Pin # | Mating | Function | |
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— | 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) |
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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 different power connector than the decades-old four-pin Molex connector found on pre-SATA devices. Like the data cable, it is wafer-based, but its wider 15-pin shape prevents accidental mis-identification and forced insertion of the wrong connector type. Native SATA devices favor the SATA power-connector, although some early SATA drives retained older 4-pin Molex in addition to the SATA power connector.
SATA features more pins than the traditional connector for several reasons:
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.
SATA 2.6 first defined the slimline connector, intended for smaller form-factors; e.g., notebook optical drives.
Pin # | Function | |
---|---|---|
1 | Device presence | |
2 | 5 V | |
3 | ||
4 | Manufacturing diagnostic | |
5 | Ground | |
6 |
The micro connector originated with SATA 2.6. It is intended for 1.8-inch hard drives. There is also a micro data connector, which is similar to the standard data connector, but is slightly thinner.
Pin # | Function | |
---|---|---|
1 | 3.3 V | |
2 | ||
3 | Ground | |
4 | ||
5 | 5 V | |
6 | ||
7 | Reserved | |
8 | Vendor specific | |
9 |
SATA uses a point-to-point architecture. The connection between the controller and the storage device is direct.
Modern[update] PC systems usually have a SATA controller on the motherboard, or installed in a PCI or PCI Express slot. Most SATA controllers have multiple SATA ports and can be connected to multiple storage devices. There are also port expanders or multipliers that allow multiple storage devices to be connected to a single SATA controller port.
Physical transmission uses a logic encoding known as 8b/10b encoding. This scheme eliminates the need to send a separate clock signal with the data stream. The stream itself contains necessary synchronization information that allows for SATA host/drive to extract clocking. Use of 8b/10b encoding means the stream is also DC-balanced, which allows the signals to be AC-coupled.
Separate point-to-point AC-coupled LVDS links are used for physical transmission between host and drive.
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.[23] 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 cards with a SATA connector exist that allow SATA drives to connect to legacy systems without SATA connectors.
The designers of SATA aimed for backward and forward compatibility with future revisions of the SATA standard.[24]
SCSI uses a more complex bus, usually resulting in higher manufacturing costs. SCSI buses also allow connection of several drives (using multiple channels, 7 or 15 on each channel), whereas SATA allows one drive per channel, unless using a port multiplier.
SATA 3 Gbit/s offers a maximum bandwidth of 300 MB/s per device compared to SCSI with a maximum of 320 MB/s. Also, SCSI drives provide greater sustained throughput than SATA drives because of disconnect-reconnect and aggregating performance. 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 typically more expensive so they are traditionally used in servers and disk arrays where the added cost is justifiable. Inexpensive ATA and SATA drives evolved in the home-computer market, hence there is a view that they are less reliable. As those two worlds overlapped, the subject of reliability became somewhat controversial. Note that, 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.
Serial ATA in the Enterprise has increased from 21.6% in 2006 to 27.6% in 2008. http://www.serialata.org/documents/SATA-Rev-30-Presentation.pdf
Name | Raw bandwidth (Mbit/s) | Transfer speed (MByte/s) | Max. cable length (m) | Power provided | Devices per Channel |
---|---|---|---|---|---|
eSATA | 3,000 | 300[25] | 2 with eSATA HBA (1 with passive adapter) | No | 1 (15 with port multiplier) |
eSATAp | 5 V/12 V[26] | ||||
SATA 600 | 6,000 | 600[25] | 1 | No | |
SATA 300 | 3,000 | 300[25] | |||
SATA 150 | 1,500 | 150[25] | 1 per line | ||
PATA 133 | 1,064 | 133.5 | 0.46 (18 in) | No | 2 |
SAS 600 | 6,000 | 600[25] | 10 | No | 1 (>65k with expanders) |
SAS 300 | 3,000 | 300[25] | |||
SAS 150 | 1,500 | 150[25] | |||
FireWire 3200 | 3,144 | 393 | 100 (more with special cables) | 15 W, 12–25 V | 63 (with hub) |
FireWire 800 | 786 | 98.25 | 100[27] | ||
FireWire 400 | 393 | 49.13 | 4.5[27][28] | ||
USB 3.0* | 4,000 | 400[25] | 3[29] | 4.5 W, 5 V | 127 (with hub)[29] |
USB 2.0 | 480 | 60 | 5[30] | 2.5 W, 5 V | |
USB 1.0 | 12 | 1.5 | 3 | Yes | |
SCSI Ultra-320 | 2,560 | 320 | 12 | No | 15 (plus the HBA) |
Fibre Channel over optic fiber |
10,520 | 2,000 | 2–50,000 | No | 126 (16,777,216 with switches) |
Fibre Channel over copper cable |
4,000 | 400 | 12 | ||
InfiniBand Quad Rate |
10,000 | 1,000 | 5 (copper)[31][32]
<10,000 (fiber) |
No | 1 with point to point Many with switched fabric |
Light Peak | 10,000 | 1,250 | 100 | No | Many |
Unlike PATA, both SATA and eSATA support hot-swapping by design. However, this feature requires proper support at the host, device (drive), and operating-system level. In general, all SATA devices (drives) support hot-swapping (due to the requirements on the device-side), also most SATA host adapters support this command.[1]
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.
Serial Attached SCSI (SAS) is designed for hot-swapping.
When developing and/or troubleshooting the Serial ATA bus, examination of hardware signals can be very important to find problems. Logic analyzers and bus analyzers are tools which collect, analyze, decode, store signals so people can view the high-speed waveforms at their leisure.
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