Monday, March 26, 2012

What is SATA interface?

SATA, short for Serial ATA, is new hard disk interface standard totally different with parallel ATA. It is named for adopting serial method in data transfer. SATA bus uses embedded clock signal, possessing stronger error correcting capability. The biggest different with previous interface is that SATA can check transfer instruction (not only data) and correct errors automatically, which, in some degree, improve data transfer security. Serial interface still has advantages such as simple structure and support of hot plugging.

Merits and principles of SATA
Compared with parallel ATA, SATA boasts more merits. Firstly, Serial ATA transfers data in a serial way and just transfers 1 byte data per time to reduce SATA pin number, improving efficiency. As a matter of fact, Serial ATA only uses 4 pins to finish all tasks with each pin for connecting cable, earth wire, transferring data and receiving data respectively. Meanwhile, such infrastructure can lower system energy consumption and system complexity. Secondly, Serial ATA has high starting point and great potential. The defined data transfer of Serial ATA 1.0 reaches up to 150MB/s which is higher than the highest 133MB/s data transfer rate of current parallel ATA. Moreover, the data transfer rate of Serial ATA 2.0 can even reach 300mb/s and Serial ATA 3.0 could realize 600MB/s finally.

It is quite necessary here to explain Serial ATA data transfer rate. In terms of parallel communication, data transfer rate refers to the actual bit rate of Serial interface data transfer. Serial ATA 1.0 has 1.5 Gbps data transfer rate and Serial ATA has 3.0Gbps. Like other high-speed Serial interfaces, Serial ATA interface still adopts a set of coding mechanism to ensure data stream features. This set of coding mechanism codes original 8-bit data into 10-bit data. Thus, serial data stream of each Serial ATA byte would contain 10-bit data and Serial ATA transfer rate after coding accordingly becomes 1/10 of actual transfer rate. Therefore, 1.5Gbps equals to 150MB/sec and 3.0Gbps means 300MN/sec.

Physical design  
It is fair to say that SATA physical design is based on Fibre Channel adopting 4-core wire. The needed voltage is reduced to 250mV, which is at least 20 times lower than traditional parallel ATA. For this reason, manufacturer can add to Serial ATA hard disk advanced hard disk functions, such as Hot Swapping. What's more, aside from Point-to-Point connection mode, SATA still supports starlike connection giving high-level application such as RAID design expediency. In practical use, SATA Host Bus Adapter is like exchange board in network, communicating with each hard disk in a channel way. Namely, each SATA hard disk takes up a transmission channel independently and master/subordinate control problem on parallel ATA doesn't exist on Serial ATA.

Serial ATA specification is not only based on future, but keeps a couple of backward compatibility methods and there isn't any compatibility problem on Serial ATA. In aspect of hardware, Serial ATA standard allows using adapter to provide parallel device compatibility and the adapter can convert parallel signal coming from mother board to serial signal workable on Serial ATA. At present, such adapter is available on market in several types, which, to some degree, protects original investment and reduces upgrade cost. In aspect of software, Serial ATA and parallel ATA kept software compatibility, which means that manufacturers don't need to rewrite any driver program and operating system code.
In addition, Serial ATA wiring is much simpler in comparison with that of traditional parallel ATA, easier kept and experienced conspicuous improvement in case air flow and heat dissipation. Besides, compared with parallel ATA which was fixed within case, SATA hard disk boasts of great extensibility which can be located both externally and internally. Since SATA and fiber channel share the same design, transfer speed could be ensured with different channels. This has crucial significance on server and network storage.

Serial ATA enjoys more advantages over parallel ATA and becomes an inexpensive alternative of parallel ATA. The transition from parallel ATA to Serial ATA is an irresistible trend and is only a matter of time. Relevant manufacturers are promoting SATA interfaces, such as the South Bridge chip of Intel ICH6 series on which SATA interfaces has been increased from 2 to 4 while parallel ATA interfaces decreased from 2 to 1; nForce4 series chip group of Nvidia, which supports Serial ATA 2.0 and Samsung which has adopted Marvell 88i6525 SOC chip to have developed and released new-generation SATA II hard disk in early 2005. 

It is noteworthy that either SATA or SATA II doesn't pose qualititive effect on hard disk performance as currently hard disk bottleneck is centralized on hard disk transfer rate which is determined by hard disk internal mechanical structure, storage technology and rorating speed. Even the top 15000-roration SCSI hard disk enjoys not more than 80MB/s internal data transfer rate, let alone ordinary 7200-rotation hard disk. Unless hard disk data recording technology experices revolutionary changes, such as vertical recording technology, current hard disk internal data transfer rate can hardly enjoy dramatical enhancement. To say it a little bit nastily, ATA 100 is far enough for hard disk and the reason why technicians develop more advanced interface technology is that higher burst data transfer rate can be obtained, more features are support and more potential will be procured.

While with the development of technology, SSD technology is under rapid development and there is company which has already published SSD whose speed far surpasses HDD. Therefore, the introduction and further development of SATA and SATA II are quite essential.

Brief introduction
Short for External Serial ATA, ESATA is an extended Serial ATA 1.0a specification designed for external drive with comparatively small scale but relevant products being circulated on market.

In order to avoid misconnection, eSATA interface shape differs from that of SATA with longest connection line of 2m and transfer speed two times as fast as mainstream USB2.0. it still support hot swapping.

SATA is a subsidiary wholy funded by Danaher Group, America-a famous brand owned by Danaher Tools (Shanghai).'

The origin of "Danaher" dates back to the root "Dana" which means "torrential river" in Celtic 700 BC.

It was established in early 1980s when corporation founders traveled and fished at a southern branch of river FlatHead, west of Montana, Canada, named Danaher. The founders named this new organization with the name of the river.


By implementing key development strategy, this corporation has become the most competitive manufacturer in the industry. Danaher, America, is a listed company headquartered in Washington, DC with 8 billion sale per year. By 2005, Danaher boasts 40.000 employees from more than 20 countries and regions. Its main businesses are tools, components, programs and environments-controlling products.  

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