分类： LINUX
2007-02-12 23:17:07
In computer hardware, Serial ATA (SATA, is a computer bus technology primarily designed for transfer of data to and from a hard disk. It is the successor to the legacy Advanced Technology Attachment standard (ATA, also known as IDE). This older technology was retroactively renamed Parallel ATA (PATA) to distinguish it from Serial ATA.
The Serial ATA [SATA] bus is defined over two separate connectors, one connector for the data lines and one for the power lines. A Serial ATA Hard drive may also have a third connector for legacy PATA power connections. The PATA power connector may be used in instead of the SATA power to supply a connection which is more rugged and reliable then the SATA-1 power connection.
The Serial ATA interface [SATA] is the serial version of the IDE [ATA] spec. SATA uses a 4 conductor cable with two differential pairs [Tx/Rx], plus an additional 3 grounds pins and a separate power connector. Data runs at 150MBps [1.5GHz] using 8B/10B encoding and 250mV signal swings, with a maximum bus length of 1 meter. SATA enhancements move the data transfer speed to; 300MBps [3.0Gbps], and then 600MBps [6.0Gbps]. The current speed for SATA is 300Mbps [3Gbps]. Shielded external SATA [eSATA] data cable runs out to a maximum of between 3 feet and 6 feet. eSATA cables are used external to the chassis or case.
| Pin # | Signal Name | Signal Description |
| 1 | GND | Ground |
| 2 | A+ | Transmit + |
| 3 | A- | Transmit - |
| 4 | GND | Ground |
| 5 | B- | Receive - |
| 6 | B+ | Receive + |
| 7 | GND | Ground |
| Pin # | Signal Name | Signal Description |
| 1 | V33 | 3.3v Power |
| 2 | V33 | 3.3v Power |
| 3 | V33 | 3.3v Power, Pre-charge, 2nd mate |
| 4 | Ground | 1st Mate |
| 5 | Ground | 2nd Mate |
| 6 | Ground | 3rd Mate |
| 7 | V5 | 5v Power, pre-charge, 2nd mate |
| 8 | V5 | 5v Power |
| 9 | V5 | 5v Power |
| 10 | Ground | 2nd Mate |
| 11 | Reserved | - |
| 12 | Ground | 1st Mate |
| 13 | V12 | 12v Power, Pre-charge, 2nd mate |
| 14 | V12 | 12v Power |
| 15 | V12 | 12v Power |
| Pin # | Signal Function | 18 AWG Wire |
| 1 | +12V DC | Yellow |
| 2 | +12V Return | Black |
| 3 | +5V Return | Black |
| 4 | +5V DC | Red |
SATA signal names are with respect to the Host, the device connected to the host reverses the signal names. Transmit pins connect to Receive pins on the other device. The SATA connector is keyed at pin 1. These pin outs for the Serial ATA connector are not compatible with the legacy PATA connector.
[The following article is licensed under the GNU Free Documentation License. It reproduces the ]First-generation Serial ATA interfaces, also known as SATA/150, run at 1.5 Gigahertz (GHz). 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 Gigabits per second (Gb/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.
Soon after SATA's introduction, enhancements were made to the standard. A 3Gb/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/3Gbs devices, the latter devices are required to support the original 1.5Gb/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 150Â MB/s with the use of a jumper for a 300Â MB/s drive.
Like SATA 1.5Gb/s, SATA 3Gb/s uses 8B/10B encoding resulting in an actual data transfer rate of 2.4 Gb/s, or 300 MB/s.
The 3.0Â 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 3Gb/s specification being only one of many that the former SATA II defined, and suggests that “SATA 3Gb/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-IO plans to further increase the maximum throughput of Serial ATA to 600Â MB/s around the year 2007.
SATA 3Gb/s is sometimes also referred to as SATA/300 or SATA II, continuing the line of PATA/100, PATA/133 and SATA/150.
SATA-IO plans to make a 6.0 Gb/s standard. Although the theoretical thoroughput would be doubled, conventional hard disks can't approach saturating this speed.
SATA drops the master/slave 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.
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 8Â 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.
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 seemingly large number of pins are used to supply three different voltages if necessary — 3.3Â V, 5Â V, and 12Â V. Each voltage is supplied by three pins ganged together (and 5 pins for ground). This is because the small pins cannot supply sufficient current for some devices, so they are combined. One pin from each of the three voltages is also used for hotplugging. The same physical connections are used on 3.5-in (90mm) and 2.5-in (70mm) (notebook) hard disks. Some SATA drives include in PATA style four-pin Molex connector for use with power supplies that lack the SATA power connector. Also, adaptors are available to convert a PATA style power connector to SATA power connector.
eSATA was standardized in mid-2004, with specifically defined cables, connectors, and signal requirements for external SATA drives. eSATA is characterized by:
USB and Firewire require conversion of all communication with the external disk, so external USB/Firewire enclosures include an IDE or SATA bridge chip that translates from the ATA protocol to USB or Firewire. Drive features like S.M.A.R.T. cannot be exploited that way and the achiveable transfer speed with USB/Firewire is only about half of the entire bus data rate of about 50MB/s. This limited effective data transfer rate becomes very visible when using an external RAID array and also with fast single disks which may yield well over 70MB/s during real use.
Currently, most PC motherboards do not have an eSATA connector. eSATA may be enabled through the addition of an eSATA host bus adapter (HBA) or bracket connector for desktop systems or with a Cardbus or ExpressCard for notebooks.
Note: Prior to the final specification for eSATA, 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 IEEE 1394. These products are not eSATA compliant.
eSATA does not provide power, which means that external 2.5" disks which would otherwise be powered over the USB or Firewire cable need a separate power cable when connected over eSATA.
| eSATA | PATA | Fire Wire 1394b | USB 2.0 | |
|---|---|---|---|---|
| Actual Speed | 2.4 >Gib/s | 1064 Mib/s | 786 Mib/s | ~375 Mib/s |
| Max. cable length | 2 meters | 46 centimetres | 4.5 meters 16 cables can be daisy chained up to 72 meters |
5 meters |
| Power cable required? | Yes | Yes | No | No |
| Devices per Channel | 1 (5 with multiplier) | 3 (3rd device read only) | 63 | 127 |
The backward compatibility of SATA hard discs is virtually non-existent in the sense that SATA drives will not work with the same connectors that IDE, SCSI, or any other format of hard drive connect to. It is, however, possible to purchase convertors that attach to the rear of the SATA hard disc and will allow it to function as an IDE drive. This can prove useful in situations where one wishes to use their SATA drive on older motherboards that may not have SATA connections, etc.
SCSI currently offers transfer rates higher than SATA, but is a more complex bus usually resulting in higher costs to the user. 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.
