The Advantage of the SATA Storage Interface

The Serial Advanced Technology Attachment (SATA) computer bus is a storage-interface for connecting host bus adapters, often found in laptops and desktop motherboards to mass storage devices. SATA host adapters and peripherals communicate with each other via a high-speed serial cable.

The Serial ATA International Organization (SATA-IO) is the group responsible for developing, managing and driving adoption of SATA specifications. Users of the SATA interface benefit from greater speed, easy-to-use upgradeable storage devices and simpler configuration.

The SATA interface debuted in 2001, and it is now the most popular interface for PC applications. With data transfer rates of 1.5 Gbps, SATA 1.0 soon became a replacement for the Parallel ATA (PATA) interface. As of 2009, SATA has replaced all but legacy ATA in all consumer PCs being shipped. SATA is advantageous over PATA in several ways, including its smaller and less expensive cable, faster and more efficient data transfer and ability to hot swap, or add/remove devices while in operation.

The next generation of SATA doubled the data transfer rate to 3 Gbps. The SCSI interface had been able to accept several requests and respond to them in the order which minimized response time. This feature, called native command queuing (NCQ), was adopted as an optional feature for both SATA 1.5 Gbps and SATA 3 Gbps devices. Given the importance of backward compatibility between SATA 1.5 Gbps and SATA 3 Gbps devices, SATA 3 Gbps is designed to fall back to SATA 1.5 Gbps when in communication with SATA 1.5 Gbps devices.

eSATA
Initially, SATA was designed as an internal, inside-the-box technology; however, designers quickly realized that the interface could be expanded outside the PC, bringing the same performance and features to external storage needs. This led to the development of a new connector called external SATA or eSATA which is specified for external devices.

With eSATA, consumers can receive the same benefits that SATA brings to storage. eSATA was released as a new standard in 2004, with specifically defined cables, connectors and signal requirements. It is hot pluggable and provides more performance than existing solutions. Several benefits of eSATA include its robust and user-friendly external connection, its ability to utilize a shielded cable up to 2 meters and its cost (eSATA delivers a higher gigabyte transfer rate per dollar than existing storage interfaces and does not require a protocol translation chip).

There are a few differences between the shielded connector and the internal connector. In order to prevent the use of unshielded internal cables in external applications, the external connector has no "L" shaped key, and the guide features are offset and smaller. To prevent damage, the insertion depth has increased by 1.6 mm to 6.6 mm and the contacts are mounted back farther in the receptacle and the plug. The cable also has an extra layer of shielding and the connectors have metal contact points. Additionally, there are springs as retention features built into the connector shield on both the top and bottom surfaces.

One key advantage of eSATA over other interfaces is its speed (up to 6 times faster than USB 2.0 or 1394). As consumers continue to collect a swelling number of high resolution photographs, videos and music files, data transfer rate is increasingly important. By using an eSATA interface, end-users are able to back up their computer systems significantly faster than with existing external storage solutions.

Because SATA is the common standard interface in nearly all new hard drives, eSATA doesn't require the overhead of converting the signal between the external interface and the internal IDE drive. Rather, a buffered direct connect is all that is needed to extend the computer's internal SATA ports outside of the PC.

Applications for eSATA include external direct attached storage for notebooks, desktops, consumer electronics and entry servers, and also support for multiple streams of content such as parallel read and write on a DVR.

Looking forward to the SATA 3.0 specification
The current SATA rev. 2.x specifications detail data transfer rates up to 3.0 Gbit/s. SATA IO presented the draft specification of SATA 6 Gbit/s physical later last year. The full 3.0 standard is anticipated to be available this year. While hard disk drives hardly saturate the 1.5 Gbps bandwidth of original SATA, a move from SATA 3 Gbps to SATA 6 Gbps will benefit the flash read speeds of ONFI drives that can reach well over 500 MB/s.

The new specification will include a few extensions to the command set, namely in the area of data and command queuing, and the enhancements are geared to improve quality of service for video streaming. The standard will support distances up to one meter. The new specification may require higher power consumption for supporting chips; however, new process technologies and power management techniques are expected to combat the potential problem. The future standard will be backward compatible with SATA 2.x specifications.