Serial ATA
Un article de Vev.
Modèle:Infobox Computer Hardware Bus
Serial Advanced Technology Attachment (SATA, Modèle:IPAEng or Modèle:IPA) is a computer bus primarily designed for transfer of data between a computer and storage devices (like hard disk drives or optical drives).
The main benefits are faster transfers, ability to remove or add devices while operating (hot swapping), thinner cables that let air cooling work more efficiently, and more reliable operation with tighter data integrity checks than the older Parallel ATA interface.
It was designed as a successor to the legacy Advanced Technology Attachment standard (ATA), and is expected to eventually replace the older technology (retroactively renamed Parallel ATA or PATA). Serial ATA adapters and devices communicate over a high-speed serial cable.
Sommaire |
Advanced Host Controller Interface
The standard interface for SATA controllers is Advanced Host Controller Interface (AHCI), which allows advanced features of SATA such as hot plug 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 that are not supported by the ATA/IDE standard. Windows device drivers that are labeled as SATA are usually running in IDE emulation mode unless they explicitly state that they are AHCI. Windows XP does not officially support AHCI although some proprietary device drivers may allow it.[citation needed] Windows Vista and the current versions of Mac OS X and Linux [1] have native support for AHCI.[citation needed]
Features
SATA offers performance as high as 3.0 Gbit/sec per device with the current specification. SATA uses only 4 signal lines, allowing for much more compact (and less expensive) cables compared with PATA. It also offers new features such as hot-swapping and NCQ. There is a special connector (eSATA) specified for external devices, and an optionally implemented provision for clips on internal connectors. SATA drives may be plugged into Serial Attached SCSI (SAS) controllers and communicate on the same physical cable as native SAS disks. SAS disks, however, may not be plugged into a SATA controller.[citation needed]
Throughput
SATA 1.5 Gbit/s
First-generation SATA interfaces, also known as SATA/150 or (unofficially) as SATA 1, communicate at a rate of 1.5 gigabits per second (Gbit/s). Taking into account 8b10b coding overhead, the actual uncoded transfer-rate is 1.2 Gbit/s, or 1,200 megabits per second (Mb/s). In actual operation, SATA/150 and PATA/133 are comparable in terms of their theoretical burst-throughput. However, newer SATA devices offer enhancements (such as NCQ) to SATA's performance in a multitask environment. For comparison, the fastest modern desktop hard drives transfer data at a maximum of ~120 MB/s,<ref name="Tom_Terabyte-Battle">Samsung Spinpoint F1 HDDs: New Winners?. Tom's Hardware.</ref> which is well within the performance capabilities of even the older PATA/133 specification.
During the initial period after SATA/150's finalization, both adapter and drive manufacturers used a "bridge chip" to convert existing designs with the PATA-interface to the SATA-interface.[citation needed] Bridged drives have a SATA connector, may include either or both kinds of power connectors, and generally perform identically to native drives. They generally lack support for some SATA-specific features (such as NCQ). Bridged products gradually gave way to native SATA products.[citation needed]
SATA 3.0 Gbit/s
Soon after SATA/150's introduction, a number of shortcomings in the original SATA were observed. At the application level, SATA's operational model emulated PATA in that the interface could only handle one pending transaction at a time. SCSI disks have long benefited from the SCSI interface's support for multiple outstanding requests, allowing the drive targets to re-order the requests to optimize response time. Native command queuing (NCQ) adds this capability to SATA. NCQ is an optional feature, and may be used in both SATA 1.5 Gbit/s or SATA 3.0 Gbit/s devices.
First-generation SATA devices were scarcely faster than legacy parallel ATA/133 devices. So a 3 Gbit/s signaling rate was added to the Physical layer (PHY layer), effectively doubling data throughput from 150 MB/s to 300 MB/s. SATA/300's transfer rate is expected to satisfy drive throughput requirements for some time, as the fastest desktop hard disks barely saturate a SATA/150 link. This is why a SATA data cable rated for 1.5 Gbit/s will currently handle second generation, SATA 3.0 Gbit/s sustained and burst data transfers without any loss of performance.
Backward compatibility between SATA 1.5 Gbit/s controllers and SATA 3.0 Gbit/s devices was important, so SATA/300's autonegotiation sequence is designed to fallback to SATA/150 speed (1.5 Gbit/s rate) when in communication with such devices. In practice, some older SATA controllers do not properly implement SATA speed negotiation. Affected systems require user-intervention to manually set the SATA 3.0 Gbit/s peripherals to 1.5 Gbit/s mode, generally through the use of a jumper.<ref name="Barracuda">Barracuda 7200.10 SATA Seagate.</ref> Known faulty chipsets include the VIA VT8237 and VT8237R south bridges, and the VIA VT6420 and VT6421L standalone SATA controllers.<ref>Service and Support Western Digital.</ref> SiS's 760 and 964 chipsets also initially exhibited this problem, though it can be rectified with an updated SATA controller ROM.[citation needed]
SATA II Misnomer
The 3.0 Gbit/s specification has been very widely referred to as “Serial ATA II” (“SATA II” or “SATA2“), contrary to the wishes of the The Serial ATA International Organization (SATA-IO) which defines the standard.
SATA 6.0 Gbit/s
SATA's roadmap includes plans for a 6.0 Gbit/s standard. In current PCs, SATA 3.0 Gbit/s already greatly exceeds the sustainable (non-burst) transfer rate of even the best hard disks. The 6.0 Gbit/s standard is useful right now in combination with port multipliers, which allow multiple drives to be connected to a single Serial ATA port, thus sharing the port's bandwidth with multiple drives.<ref name=sataio_pmtech> Serial ATA Port Multiplier Technology
. SATA-IO
. Retrieved on 2007-07-12. </ref> Solid-state drives such as RAM disks may also one day make use of the faster transfer rate.
Cables and connectors
The SATA power and data cables are the most noticeable change from Parallel ATA. Unlike Parallel ATA, the same physical connectors are used on 3.5-in (90 mm) desktop hard disks and 2.5-in (70 mm) notebook disks; this eliminates the need for a mechanical adapter when using a notebook drive in a desktop computer.
| Pin # | Function |
|---|---|
| 1 | Ground |
| 2 | A+ |
| 3 | A− |
| 4 | Ground |
| 5 | B− |
| 6 | B+ |
| 7 | Ground |
| Image:SATA Data Cable.jpg | |
| A 7-pin Serial ATA 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 be up to 1 m (39 in) long, 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-conductor wires, and are limited to 45 cm (18 in) in length by the PATA specification (however, cables up to 90 cm (36 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, but cables can be purchased that have a 'locking' feature, whereby a small (usually metal) spring holds the plug in the socket.
| Pin # | Function | |
|---|---|---|
| 1–3 | 3.3V | |
| 4–6 | Ground | |
| 7–9 | 5V | |
| 10 | Ground | |
| 11 | Staggered spinup (in supporting drives) | |
| 12 | Ground | |
| 13–15 | 12V | |
| Image:SATA power cable.jpg | ||
| A 15-pin Serial ATA power connector. | ||
The SATA standard also specifies a new power connector. Like the data cable, it is wafer-based, but its wider 15-pin shape prevents accidental misidentification and forced insertion of the wrong connector type. Native SATA devices favor the SATA power-connector over the old four-pin Molex connector (found on all PATA equipment), although some SATA drives retain older 4-pin Molex. The SATA/power connector has been criticized for its poor robustness—the thin plastic tops of the connectors (see power connector picture at right) can break due to shearing force when the user pulls the plug at a non-orthogonal angle. The seemingly large number of pins are used to supply three different voltages: 3.3 V, 5 V, and 12 V. Each voltage is supplied by three pins ganged together, while ground is provided by five pins. Each pin should be able to provide 1.5 A. Pin 11 is used in newer drives for staggered spinup. The supply pins are ganged together because the small pins by themselves cannot supply sufficient current for some devices. One pin from each of the three voltages is also used for hotplugging.
Adaptors are available to convert a 4-pin Molex connector to SATA power connector. However, because the 4-pin Molex connectors do not provide 3.3 V power, these adapters provide only 5 V and 12 V power and leave the 3.3 V lines disconnected. This precludes the use of such adapters with drives that require 3.3 V power. Understanding this, drive manufacturers have largely left the 3.3 V power lines unused. However, without 3.3 V power, the SATA device may not be able to implement hotplugging as mentioned in the previous paragraph.
External SATA
Standardized in mid-2004, eSATA defined separate cables, connectors, and revised electrical requirements for external applications:
- 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 m (USB and FireWire allow longer distances.)
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 almost 120 MB/s during real use,<ref name="Tom_Terabyte-Battle"/> more than twice the maximum transfer rate of USB 2.0 or FireWire 400 (IEEE 1394a) and well in excess of the maximum transfer rate of FireWire 800, though the S3200 FireWire 1394b spec reaches ~400 MB/s. Finally, some low-level drive features, such as S.M.A.R.T., are not usable through USB or FireWire bridging.<ref> Questions about the indicators of health/performance (in percent)
. HDDlife
. Retrieved on 2007-08-29. </ref> eSATA does not suffer from these issues.
eSATA will likely co-exist alongside USB 2.0 and FireWire storage for several reasons. The ubiquity of USB ports on all mass-market computers, and FireWire ports on many consumer electronic appliances, guarantee a large market for USB and FireWire storage.[citation needed] For small form-factor devices (such as external 2.5" (70 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.
As of 2007, an eSATA external drive enclosure will typically ship with a passive eSATA-to-SATA bracket/cable-adapter to install on desktops that lack an eSATA port or that need another. Desktops can also be upgraded with the installation of an eSATA host bus adapter (HBA), while notebooks can be upgraded with Cardbus<ref name="addonics_cardbus">CardBus SATA adapter</ref> or ExpressCard<ref name="addonics_expresscard">ExpressCard SATA adapter</ref> versions of an eSATA HBA. With passive-adapters, the maximum cable length is reduced to 1 meter, 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.[citation needed]
eSATA may be ignored by the enterprise and server market, which has already standardized on the separately-developed Serial Attached SCSI (SAS) interface, which has extra features for remote management, link redundancy, and link monitoring.[citation needed] The eSATA hotplug capability and consumer-level price-point combination, however, may result in a larger eSATA market share in the enterprise and server market space than would otherwise be expected.
Note: Prior to the final eSATA specification, there were a number of products 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 manipulation. It's similar to the regular SATA connector, but with reinforcements in both the male and female sides, inspired by the USB connector. It's harder to unplug and can withstand a cable being yanked or wiggled. On a SATA connector, this kind of action will break the male side of the connection (the hard drive or host adapter), rendering the device unusable. With an eSATA connector, considerably more force is needed to damage the connector, and even in this situation, only the female side (the cable itself) will break, possibly leaving the male usable.[citation needed]
Backward and forward compatibility
SATA and PATA
At the device level, SATA and PATA devices are completely incompatible—they cannot be interconnected. At the application level, SATA devices are specified to look and act like PATA devices.<ref>
A comparison with Ultra ATA Technology (PDF) . SATA-IO
. Retrieved on 2007-07-12. </ref> In early motherboard implementations of SATA, backward compatibility allowed SATA drives to be used as drop-in replacements for PATA drives, even without native (driver-level) support at the operating system level.
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.
Powered enclosures are available for both PATA and SATA drives, which interface to the PC through USB, Firewire or eSATA, with the restrictions noted above. PCI cards with a SATA connector exist that allow SATA drives to connect to legacy systems without SATA connectors.
SATA 1.5Gb/s and SATA 3Gb/s
SATA is designed to be backward and forward compatible with future revisions of the SATA standard.<ref>Serial ATA - Next Generation Storage Interface Hitachi Global Storage Technologies.</ref>
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 which was manufactured in 2003, do not support SATA 3Gb/s drives. To address interoperability problems, the largest hard drive manufacturer Seagate/Maxtor have added a user-accessible jumper-switch known as the Force 150, to switch between 150 MB/s and 300 MB/s operation.<ref name="Barracuda">Barracuda 7200.9 SATA Seagate.</ref> Users with a SATA 1.5Gb/s motherboard with one of the listed chipsets should either buy an ordinary SATA 1.5Gb/s hard disk, buy a SATA 3Gb/s hard disk with the user-accessible jumper, or buy a PCI or PCI-E card to add full SATA 3Gb/s capability and compatibility. Western Digital uses jumper setting called "OPT1 Enabled" to force 150 MB/s data transfer speed.
Comparisons with other interfaces
SATA and SCSI
SCSI currently offers transfer rates higher than SATA, but is a more complex bus usually resulting in higher manufacturing cost. Some drive manufacturers offer longer warranties for SCSI devices, however, indicating a possibly higher manufacturing quality control of SCSI devices compared to PATA/SATA devices. 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 port multiplier.
SATA 3.0 Gbit/s offers a maximum bandwidth of 300 MB/s per device compared to SCSI with a maximum of 320 MB/s. Also, SCSI drives provide greater sustained throughput than SATA drives because of disconnect-reconnect and aggregating performance. SATA devices are generally compatible with SAS enclosures and adapters, while SCSI devices cannot be directly connected to a SATA bus.
SCSI, SAS and FC drives are typically more expensive, as they are traditionally used in servers and disk arrays. Inexpensive ATA and SATA drives evolved in the home computer market, hence the general opinion is that they are less reliable. As those two worlds started to overlap, the subject of reliability became somewhat controversial. It is worth noting that generally a disk drive has a low failure rate because of increased quality of its heads, platters and supporting manufacturing processes, not because of having a certain interface.
eSATA in comparison to other external buses
| Raw bandwidth (Mbit/s) | Transfer speed (MB/s) | Max. cable length (m) | Power provided | Devices per Channel | |
|---|---|---|---|---|---|
| SAS | 3000 | 375 | 8 | Modèle:No | 4 |
| eSATA | 3000 | 375 | 2 | Modèle:No | 1 (15 with port multiplier) |
| SATA 300 | 3000 | 375 | 1 | Modèle:No | 1 per line |
| SATA 150 | 1500 | 187.5 | 1 | Modèle:No | 1 per line |
| PATA 133 | 1064 | 133 | 0.46 (18 inches) | Modèle:No | 2 |
| FireWire 3200 | 3144 | 393 | 4.5<ref name="16 cables">16 cables can be daisy chained up to 72 m</ref>, alternate cables available for 100m+ | Modèle:Yes | 63 |
| FireWire 800 | 786 | 98.25 | 4.5<ref name="16 cables">16 cables can be daisy chained up to 72 m</ref> | Modèle:Yes | 63 |
| FireWire 400 | 393 | 49.13 | 4.5<ref name="16 cables" /> | Modèle:Yes | 63 |
| USB 2.0 | 480 | 60 | 5<ref name="USB">USB hubs can be daisy chained up to 25 m</ref> | Modèle:Yes | 127 |
| USB 3.0 | 4800 | 600 | TBD, uses new cabling integrating fiber optics with copper | Modèle:Yes | 127 |
| Ultra-320 SCSI | 2560 | 320 | 12 | Modèle:No | 16 |
| Fiber Channel over copper cable | 4000 | 400 | 12 | Modèle:No | 126 (16777216 with switches) |
| Fiber Channel over fiber | 10520 | 2000 | 2–50000 | Modèle:No | 126 (16777216 with switches) |
Unlike PATA, both SATA and eSATA are designed to support hot-swapping. 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), but requisite support is less common on SATA host adapters.[citation needed]
USB allows hot-swapping; this is supported by virtually every current operating system. However, USB-based storage hardware can infrequently sustain data loss when disconnected. This problem exists with media players and digital cameras using flash memory as well as mobile 2.5-inch USB hard drives.[citation needed] Firmware damage and data loss can occasionally result from unclean spin-downs and power loss when the drive or device is removed from the USB port without first initiating a device shutdown via the computer's operating system.<ref>USB 2.0 Storium Drive HANBiT Electronics Company.</ref>
SCSI devices with SCA-2 connectors are designed for hot-swapping. Many server and RAID systems provide hardware support for transparent hot-swapping. The SCSI standard prior to SCA-2 connectors was not designed for hot-swapping, but, in practice, most RAID implementations support hot-swapping of hard disks.
Serial Attached SCSI (SAS) is designed for swapping.
See also
- Advanced Host Controller Interface (AHCI)
- AT Attachment (ATA)
- Compare SATA Bandwidth
- Compare eSATA Bandwidth
- Native Command Queuing (NCQ)
Notes and references
External links
- Serial ATA International Organization ( SATA-IO )
- "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 3Gb/s
- Modèle:PDFlink
- SATA motherboard connector pinout
- AHCI/RAID Intel® Matrix Storage Technology: Unattended installation instructions under Windows XP
- Intel® Matrix Storage Manager: How do I install an operating system on single serial ATA hard drive?bs:SATA
cs:SATA de:Serial ATA el:SATA es:Serial ATA eo:Serial ATA fr:Serial ATA gl:Serial ATA ko:SATA it:Serial ATA he:Serial ATA hu:Serial ATA lt:Serial ATA nl:Serial ATA ja:シリアルATA no:Serial ATA pl:SATA pt:Serial ATA ru:SATA simple:Serial ATA sk:Serial ATA sr:САТА fi:Serial ATA sv:Serial ATA tr:SATA zh:SATA
Catégories de la page: All articles with unsourced statements | Articles with unsourced statements since July 2007 | Articles with invalid date parameter in template | Articles with unsourced statements since January 2007 | Articles with unsourced statements since February 2007 | Serial ATA | Computer buses
