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SATA redirects here. For other uses of the word SATA, see SATA (disambiguation) In computer hardware, Serial ATA (SATA, or ) is a computer bus technology primarily designed for transfer of data to and from a hard disk. It is the successor to the legacy AT Attachment standard (ATA). This older technology was retroactively renamed Parallel ATA (PATA) to distinguish it from Serial ATA. Both SATA and PATA drives are IDE (Integrated Drive Electronics) drives, although IDE is often misused to indicate PATA drives. SATA 1.5 Gb/s First-generation SATA interfaces, also known as SATA/150 or SATA 1, run at 1.5 gigabits per second (Gb/s). Serial ATA uses 8B/10B encoding at the physical layer. This encoding scheme has an efficiency of 80%, resulting in an actual data transfer rate of 1.2 Gbit/s, or 150 megabytes per second (MB/s). The relative simplicity of a serial link and the use of LVDS allow both the use of longer drive cables and an easier transition path to higher speeds. SATA 3.0 Gb/s Soon after SATA's introduction, enhancements were made to the standard. A 3 Gb/s signalling rate was added to the PHY layer, offering up to twice the data throughput. To ensure seamless backward compatibility between older SATA and the newer faster SATA 3.0 Gb/s devices, the latter devices are required to support the original 1.5 Gb/s rate. In practice, some older SATA systems that do not support SATA speed negotiation require the peripheral drive's speed be manually hardlimited to 150 MB/s with the use of a jumper for a 300 MB/s drive. This jumper setting is needed in the VIA VT8237 and VT8237R south bridges.The VIA VT6420 and VT6421L chips for add in cards are affected too.The VT8237 and VT8237R chips for example not only do not detect the 300 MB/s hard disk drives, they do not let the disk spin up either. This behaviour is not altered even if you hack your mainboard or flash the add in card BIOS and add the latest VIA SATA RAID ROM.VIA needed 3 chips in order to finally support 300 MB/s hard disk drives with VT8237+ south bridge.The jumper setting is needed in the SiS SiS964 south bridge.Also the nVIDIA nForce 2 MCP RAID and nForce 2 MCP Gigabit south bridges used in nVIDIA nForce 2 need the jumper setting.Contrary to the VIA chips,the SiS964 can work fine with newer 300 MB/s hard disk drives if you hack your mainboard BIOS and add the latest SiS SATA RAID ROM. Despite that very few mainboard manufacturers supply mainboard BIOSes with the latest SiS SATA RAID ROM in their old SiS based motherboards...** Like SATA 1.5 Gb/s, SATA 3.0 Gb/s uses 8B/10B encoding resulting in an actual data transfer rate of 2.4 Gb/s, or 300 MB/s. The 3.0 Gb/s specification has been very widely referred to as “Serial ATA II” (“SATA II”), contrary to the wishes of the Serial ATA standards organization that authored it. The official website notes that SATA II was in fact that organization's name at the time, the SATA 3.0 Gb/s specification being only one of many that the former SATA II defined, and suggests that “SATA 3.0 Gb/s” be used instead. (The Serial ATA standards organization has since changed names, and is now “The Serial ATA International Organization”, abbreviated SATA-IO.) SATA 3.0 Gb/s is sometimes also referred to as SATA 3.0 or SATA/300, continuing the line of PATA/100, PATA/133 and SATA/150. Future design: SATA 6.0 Gb/s SATA-IO plans to make a 6.0 Gb/s standard. Although the theoretical throughput would be doubled, conventional hard disks cannot approach saturating this speed. The 6.0 Gb/s standard will however be useful in combination with port multipliers, which allow multiple drives to be connected to one Serial ATA port, as well as with solid-state drives such as RAM disk. Practical Benefits In actual use in modern personal computers both SATA 3 Gb/s and SATA 1.5 Gb/s hard disk drives run at non-burst speeds comparable to earlier IDE interfaces (under 50 MB/s). Since the theoretical burst speeds marketed by drive manufacturers are rarely achieved, a smaller power and interface cable plus the ability to hot-plug are the most practical SATA benefits to everyday computing. Serial ATA innovations SATA drops the shared bus of PATA, giving each device a dedicated cable and dedicated bandwidth. While this requires twice the number of host controllers to support the same number of SATA devices, at the time of SATA's introduction this was no longer a significant drawback. Another controller could be added into a controller ASIC at little cost beyond the addition of the extra seven signal lines and printed circuit board (PCB) space for the cable header. Features allowed for by SATA but not by PATA include hot-swapping and native command queueing. To ease their transition to SATA, many manufacturers have produced drives which use controllers largely identical to those on their PATA drives and include a bridge chip on the logic board. Bridged drives have a SATA connector, may include either or both kinds of power connectors, and generally perform identically to native drives. They may, however, lack support for some SATA-specific features. As of 2004, all major hard drive manufacturers produce either bridged or native SATA drives. 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. Cables and Connectors Physically, the SATA power and data cables are the most noticeable change from Parallel ATA. The SATA standard defines a data cable using seven conductors and 8 mm wide wafer connectors on each end. SATA cables can be up to 1 m (39 in) long. PATA ribbon cables, in comparison, carry either 40- or 80-conductor wires and are limited to 46 cm (18 in) in length. The reduction in conductors makes SATA connectors and cables much narrower than those of PATA, thus making them more convenient to route within tight spaces and reducing obstructions to air cooling. Unlike early PATA connectors, SATA connectors are keyed — it is not possible to install cable connectors upside down without considerable force, and probably critically damaging one or both connectors. The SATA standard also specifies a power connector sharply differing from the four-pin Molex connector used by PATA drives and many other computer components. Like the data cable, it is wafer-based, but its wider 15-pin shape should prevent confusion between the two. The power connector is known to be quite flimsy, as the thin plastic tops of the connectors (see power connector picture at right) will often break off when even the slightest force is used to wiggle it whilst it is plugged in (as is often required in tight spaces), rendering the connector useless. The seemingly large number of pins are used to supply three different voltages if necessary — 3.3 V, 5 V, and 12 V. Each voltage is supplied by three pins ganged together, of remaining pins 5 are for ground. The last pin, 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. The same physical connections are used on 3.5-in (90 mm) and 2.5-in (70 mm) (notebook) hard disks. Some SATA drives include a PATA-style 4-pin Molex connector for use with power supplies that lack the SATA power connector. 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 3.3V power, the SATA device will not be able to implement hotplugging as mentioned in the previous paragraph. External SATA
eSATA compared to other buses Backward compatibility The backward compatibility of SATA hard disks is virtually non-existent in the sense that SATA-native drives feature both power and data connectors that are incompatible with the connectors used by PATA, SCSI, or any other format of hard drive. However, there are converters that attach to a SATA hard disk allowing it to function as a PATA drive. Some drives come with both SATA and molex power connectors. There are also powered enclosures that hold a SATA drive and act as external USB devices, with the restrictions noted above. New devices on the market enable some backward compatibility as of October, 2006. PCI cards with a SATA connector that allow SATA drive to connect to legacy systems without SATA connectors. SATA vs 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 (up to 16 or even 127) whereas SATA only allows one per cable. SATA 3.0 Gb/s offers a maximum bandwidth of 300 MB/s per device compared to SCSI with a maximum of 320 MB/s per bus. SATA 2 devices are generally compatible with SAS enclosures and adapters, while SCSI devices cannot be directly connected to a SAS bus. See also | |||||||||
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