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SATA

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"SATA" redirects here. For other uses, see SATA (disambiguation).
SATA
Serial ATA
First generation (1.5 Gbit/s) SATA ports on a motherboard
Year created2003
No. of devices1
Speed1.5 Gbit/s, 3.0 Gbit/s
StyleSerial
Hotplugging interfaceYes
External interfaceYes, with eSATA
Websitesata-io.org

Serial Advanced Technology Attachment (SATA, /ˈseɪtə/ or /ˈsætə/) is a computer bus primarily designed for transfer of data between a computer and mass storage devices such as hard disk drives and optical drives.

The main advantages over the older parallel ATA interface are faster data transfer, 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.

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.

Advanced Host Controller Interface

Main article: 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. While the drivers included with Windows XP do not support AHCI, AHCI has been implemented by proprietary device drivers.[1] 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.

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 multitasking environment. For comparison, the fastest modern desktop hard drives transfer data at a maximum of ~120 MB/s,[2] 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.[3] Known faulty chipsets include the VIA VT8237 and VT8237R south bridges, and the VIA VT6420 and VT6421L standalone SATA controllers.[4] SiS's 760 and 964 chipsets also initially exhibited this problem, though it can be rectified with an updated SATA controller ROM.[citation needed]


This table shows the real speed of SATA 1.5 Gb/s and SATA 3 Gb/s:

SATA 1.5 Gb/s SATA 3 Gb/s
Frequency 1500 MHz 3000 MHz
Bits/clock 1 1
8b10b encoding 80% 80%
bits/Byte 8 8
Real speed 150 MB/s 300 MB/s


SATA II Misnomer

The 3.0 Gbit/s specification has been widely referred to as "Serial ATA II" ("SATA II" or "SATA2"), contrary to the wishes of the Serial ATA International Organization (SATA-IO) which defines the standard. SATA II was originally the name of a committee defining updated SATA standards, of which the 3 Gb/s standard was just one. However since it was among the most prominent features defined by the former SATA II committee, the name SATA II became synonymous with the 3 Gb/s standard, so the group has since changed names to the Serial ATA International Organization, or SATA-IO, to avoid further confusion.

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 fastest 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.[5] 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; compared to the older parallel ATA, this eliminates the need for a connector adapter when using a notebook drive in a desktop computer.

Data

Pin # Function
1 Ground
2 A+
3 A−
4 Ground
5 B−
6 B+
7 Ground
A 7-pin Serial ATA data cable.
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.

Parallel ATA uses single ended signalling. In this system, the noise is amplified with the data signal during the signal transmission. Noise causes significant interference with the data signal at higher speeds. In order to reduce the noise interference, the driving voltage of Parallel ATA is as high as 5V. Although the higher voltage can reduce the noise interference, the 5V is too high for modern high speed silicon devices. Thus the fabrication cost of driving ICs is higher, and the speed is limited in comparison to low voltage silicon ICs.

In comparison, SATA systems use differential signalling. In this system, it is easy to filter out the noise from data signal during the signal transmission. The higher noise rejection allows the SATA system to use only 500mV peak-to-peak differential voltage to carry the signal at higher speeds without distortion or noise interference.

Compared with the 5V driving voltage in PATA ribbon cables, the 0.5V in SATA cables make the SATA system much more power efficient.

Power

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
A 15-pin Serial ATA power connector.
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[citation needed]—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

File:ESATA Logo.jpg
The official eSATA logo

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.)
  • The external cable connector is a shielded version of the connector specified in SATA 1.0a with these basic differences:
  • The External connector has no “L” shaped key, and the guide features are vertically offset and reduced in size. This prevents the use of unshielded internal cables in external applications.
  • To prevent ESD damage, the insertion depth is increased from 5mm to 6.6mm and the contacts are mounted further 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.
  • There are springs as retention features built into the connector shield on both the top and bottom surfaces.
  • The external connector and cable are designed for over five thousand insertions and removals while the internal connector is only specified to withstand five.
SATA (left) and eSATA (right) 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 almost 120 MB/s during real use,[2] 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., may not be available through USB or FireWire bridging.[6] eSATA does not suffer from these issues.

HDMI, Ethernet, and eSATA ports on a Sky HD Digibox

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. 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[7] or ExpressCard[8] 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]

From the second half of 2008, SATA-IO expects eSATA to provide power to eSATA devices without the need for a separate power connection. In a news release from 2008-01-14, SATA-IO calls it the "Power Over eSATA initiative."

Because of its hotplug capability and consumer-level price-point combination eSATA may be of interest to the enterprise and server market, which has already standardized on the separately-developed Serial Attached SCSI (SAS) interface.

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]

Topology

SATA topology: host – expansor - device

SATA is a point to point architecture. The connection between the controller and the storage device is direct.

In a modern PC system, the SATA controller is usually found on the motherboard, or installed in a PCI slot. Some SATA controllers have multiple SATA ports and can be connected to multiple storage devices. There are also port expanders which allow multiple storage devices to be connected to a single SATA controller port.

Encoding

These high-speed transmission protocols use a logic encoding known as 8b10b. The signal is sent using Non-return to Zero (NRZ) encoding with Low Voltage Differential Signaling (LVDS).

In the 8b10b encoding the synchronizing signal is included in the data sequence. This technique is known as Clock Data Recovery, because it doesn't use separate synchronizing signal, because it utilizes the signal 0 to 1 transitions to recover the clock signal.

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.[9] 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.[10]

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.[3] 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 a 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 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 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

Name Raw bandwidth (Mbit/s) Transfer speed (MB/s) Max. cable length (m) Power provided Devices per Channel
SAS 3000 375 8 No 4
eSATA 3000 375 2 No 1 (15 with port multiplier)
SATA 300 3000 375 1 No 1 per line;

revision 2.6 (15 with port multiplier)

SATA 150 1500 187.5 1 No 1 per line
PATA 133 1064 133 0.46 (18 inches) No 2
FireWire 3200 3144 393 100; alternate cables available for 100m+ 15 W, 12–25 V 63
FireWire 800 786 98.25 100[11] 15 W, 12–25 V 63
FireWire 400 393 49.13 4.5[12][13] 15 W, 12–25 V 63
USB 2.0 480 60 5[14] 2.5 W, 5 V 127
USB 3.0 4800 600 TBD (To Be Determined), uses new cabling integrating fiber optics with copper 2.5 W, 5 V 127
Ultra-320 SCSI 2560 320 12 No 16
Fibre Channel
over copper cable 		4000 400 12 No 126
(16777216 with switches)
Fibre Channel
over fiber 		10520 2000 2–50000 No 126
(16777216 with switches)
Infiniband
12X Quad-rate 		120000 12000 5 (copper)[15][16]

<10000 (fiber)

No 1 with Point to point
Many with switched fabric

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.[17]

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

Wikimedia Commons has media related to Serial ATA.

Notes and references

  1. ^ Intel Matrix Storage Technology. Intel Support.
  2. ^ a b Samsung Spinpoint F1 HDDs: New Winners?. Tom's Hardware.
  3. ^ a b Barracuda 7200.10 SATA Seagate. Cite error: The named reference "Barracuda" was defined multiple times with different content (see the help page).
  4. ^ Service and Support Western Digital.
  5. ^ "Serial ATA Port Multiplier Technology". SATA-IO. Retrieved 2007-07-12.
  6. ^ "Questions about the indicators of health/performance (in percent)". HDDlife. Retrieved 2007-08-29.
  7. ^ CardBus SATA adapter
  8. ^ ExpressCard SATA adapter
  9. ^ "A comparison with Ultra ATA Technology" (PDF). SATA-IO. Retrieved 2007-07-12.
  10. ^ Serial ATA - Next Generation Storage Interface Hitachi Global Storage Technologies.
  11. ^ http://developer.apple.com/documentation/HardwareDrivers/Conceptual/HWTech_FireWire/Articles/FireW_concepts.html#//apple_ref/doc/uid/TP40003893-SW16_1200331173
  12. ^ http://developer.apple.com/documentation/HardwareDrivers/Conceptual/HWTech_FireWire/Articles/FireW_concepts.html#//apple_ref/doc/uid/TP40003893-SW14_1200331173
  13. ^ 16 cables can be daisy chained up to 72 m
  14. ^ USB hubs can be daisy chained up to 25 m
  15. ^ Minich, Makia (2007-06-25). "Infiniband Based Cable Comparison" (PDF). Retrieved 2008-02-11. {{cite web}}: Check date values in: |date= (help)
  16. ^ Feldman, Michael (2007-07-17). "Optical Cables Light Up InfiniBand". HPCwire. Tabor Publications & Events. p. 1. Retrieved 2008-02-11. {{cite news}}: Check date values in: |date= (help)
  17. ^ USB 2.0 Storium Drive HANBiT Electronics Company.
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