SATA 3Gb/s

SATA 3Gb/s interface speed enables up to 300MB/s data transfer rates.

* SATA 3Gb/s enables the highest level of performance, while maintaining desktop cost structures.

* SATA 3Gb/s facilitates bandwidth aggregation for multiple devices, enabling max throughput as well as, higher cache through put performance in single drive configurations.

* 100% backward compatible with 1.5Gb/s SATA.

* No software, driver or cable upgrades required.

What is SATA 3Gb/s?

SATA 3Gb/s is the next generation of Serial ATA interface speed. This advanced optional feature is one of 8 specifications published by the previous Serial ATA Working Group II. Since the optional specifications are advanced additions to the core specification (Serial ATA 1.0a) and authored by the 2nd Serial ATA working group they were quickly nick-named SATA II. The most important fact that system builders and consumers must keep in mind is that SATA II is not synonymous with 3Gb/s. Since the advanced features are optional and referred to as SATA II by the industry, SATA II could mean any or all of these specifications. It is not recommended that vendors use SATA II to describe their SATA solutions. To read more about this view the product naming guidelines.

SATA 3Gb/s is double the speed of the current SATA interface of 1.5Gb/s. SATA 3Gb/s enables the highest level of performance while maintaining desktop cost structures.

The Serial ATA bus & bandwidth design

In contrast to Ultra ATA’s parallel bus design, Serial ATA uses a single signal path to transmit data serially, or bit by bit, and a second serial path to return receipt acknowledgements to the sender. Because each signal path is a 2-wire differential pair, the Serial ATA bus consists of 4 signal lines per channel.

The 16-bit wide parallel Ultra ATA bus is capable of transmitting two bytes of data per clock. Though Serial ATA transmits only a single bit per clock, the serial bus may be run at a much higher speed to compensate for the loss of parallelism. Serial ATA was introduced with a bandwidth of 1500Mbits/sec, or 1.5Gbits/sec. Because data is encoded using 8b/10b encoding (an 80% efficient encoding used with digital differential signaling to maintain a constant average “DC” bias point), the effective maximum throughput is 150Mbytes/sec.

Ultra ATA/100

25MHz strobe

x 2 for double data rate clocking

x 16 for bits per edge

/ 8 bits per byte

= 100 Mbytes/sec

SATA 1.5Gb/s

1500MHz embedded clock

x 1 bit per clock

x 80% for 8b10b encoding

/ 8 bits per byte

= 150 Mbytes/sec

SATA 3Gb/s

3000MHz embedded clock

x 1 bit per clock

x 80% for 8b10b encoding

/ 8 bits per byte

= 300 Mbytes/sec

Storage Arrays love SATA 3Gb/s interface speed

For host interfaces, the 3Gbits/sec speed is necessary to meet the increasing performance requirements for bandwidth-intensive applications such as disk to disk backup, video editing, medical imaging, research and near-line data storage as the amount of data that companies need to store, manage and keep readily available continues to increase. Serial ATA can help meet rising data throughput needs via the introduction of SATA 3Gb/s, enabling the transfer of more than the current 1.5 gigabits of data in aggregated arrays and other multi-drive configurations. From the host side, SATA 3Gbits/sec essentially provides a larger pipe to move data faster.

Even though the interface speed itself is a small portion of the overall drive performance and single drive performance increases may not be as noticeable with typical office applications. 3-Gbits/sec interface on the disc drive can increase system performance when the application takes advantage of the drive’s cache burst ability. In the case of writes, if the drive’s write cache capability is enabled, any write that fits in the buffer will be transferred at the full 3 Gbits/sec into the buffer. In the case of reads, caching helps when the data requested is small enough to fit into the drive cache and is present in the cache at the time of the request. That data will be transferred to the host at the full 3-Gbits/sec rate. In either case, the data must be in the form of small, sequential or near-sequential files, such as those found in some video editing applications. The reason: small sequential or near-sequential file transfers require less mechanical movement or seek overhead and maximize caching capabilities of the drive. In these types of applications, 3-Gbits/sec drive interface rates can greatly increase performance. This cache performance increase may enable larger cache sizes in the future.

Serial ATA 3Gb/s Value

As always the case, starting with the earlier times of the Parallel ATA interface, the industry attempts to avoid the limiting factor for the speed at which data are transferred to and from the disc drive. If the interface pipe is not fast enough for the disk drive’s data rate the system becomes bogged down by the interface bottleneck causing performance degradation. To stay ahead of the data rate the interface rate typically leads by at least one year. In the case of SATA 3Gb/s, customers can now experience greater than 150MB/s data rates in aggregated bandwidth and increased cache burst rate performance with single drive configurations.