Serial Data Transfer Mode (SATA) in HDD
SATA (Serial ATA) specification, describing a serial data exchange mode, was presented for the first time on Intel Developer Forum in 2000 and was finally developed to the version 1.0 at the end of the same year. The first products appeared in 2001, and the mass production was started in 2002-2003. The new serial interface is completely compatible with a traditional parallel interface. The same registers and commands are used to it that provides compatibility with the previous versions of ATA.
In SATA there is no necessity to use a jumpers of hard disk drives for configuration of a role of the disk drive in channel ATA as the master or slave device since all the hard drives are connected by an independent informational cable consisting of 7 wires, 3 from which are not used and remained 4 wires are used in pairs (one pair for transfer, another for receiving). The cable became thin and round that has allowed lowering the temperature of components in a system unit of the computer by cooling improvement. Now the plug constructively provides the protection against the wrong connection. Before the universal appearance of plugs for SATA in power supply units, the changed plug of power supply was a trouble since it was necessary to use an additional adapter. It negatively affected the reliability since the number of contacts in an HDD feed circuit increased, and modern storage devices are the powerful consumers of energy, especially at the moment of engine start.
In parallel ATA interface signals with 5-volt amplitude are used, and providing such power on an output of the chips consuming less power became difficult. Staying of SATA cable near the sources of strong electromagnetic interferences is undesirable since in SATA cable the level of signals is lowered to 0.4 volts that led to noise immunity-lowering at an information transfer. Support of connection and replacement of hard disk drives without computer turn off is described in the standard optionally, and manufacturers of hard drives began to realize it at their own discretion that led to various problems of compatibility.
Despite assurances of sellers, SATA does not increase the performance of hard disk drives, and the first market wave of the hard drives compatible with SATA had even the worse performance in comparison with completely similar devices using the classical parallel interface. Besides, the widely advertised technology of command queuing optimization (NCQ) did not bring performance increase in comparison with TCQ technology earlier used in ATA and SCSI.
SATA-2 enhancements are intended to improve the reliability of this system and require processing optimization; however innovations are designed for application not in desktop computers, but in servers. SATA-2 throughput is 300 megabytes per second. What for was it required to increase the speed of the bus when the modern HDD is capable of using no more than 60-70 percent from SATA throughput? The matter is that SATA-2 specification provides a possibility of connection of several storage devices to one port by means of the so-called hub or the port multiplier. Thus, the number of cable connections decreases, the place is saved and the possibility of flexible scaling of the system is reached. All it excites contradictory feelings. Many people remember that SATA was initially advertised as the interface simple in use, i.e. it was possible to connect only one device to each port that eliminates all the problems with the installation of jumpers, after all, such concepts, as Master and Slave with reference to disk drives disappear. It is clear that it is an attempt to take advantage of already ready and fulfilled technology for reduction in the price of servers. However, from the point of view of the consumer such decision looks a little strange.
The SATA 3.0 Revision interface provides a 6 Gbps connection. The SATA 3.0 also provides connectivity to external storage devices in its eSATA port variant. It is 100% backward compatible with devices that support the SATA 150 MB/s and SATA-2 300 MB/s standards. Some of the standard's key enhancements:
- A new Native Command Queuing (NCQ) streaming command to enable isochronous data transfers for bandwidth-hungry audio and video applications.
- An NCQ Management feature that helps optimize performance by enabling host processing and management of outstanding NCQ commands.
- Improved power management capabilities.
- A small Low Insertion Force (LIF) connector for more compact 1.8-inch storage devices.
- A connector designed to accommodate 7mm optical disk drives for thinner and lighter notebooks.