Conn-Link Technology Inc

Serial ATA Specification

SATA revision 1.0 (SATA 1.5 Gbit/s)

First-generation SATA interfaces, now known as SATA 1.5 Gbit/s, communicate at a rate of 1.5 Gbit/s, and do not support NCQ. Taking 8b/10b encoding overhead into account, they have an actual uncoded transfer rate of 1.2 Gbit/s (150 MB/s). The theoretical burst throughput of SATA 1.5 Gbit/s is similar to that of PATA/133, but newer SATA devices offer enhancements such as NCQ, which improve performance in a multitasking environment.

During the initial period after SATA 1.5 Gbit/s finalization, adapter and drive manufacturers used a "bridge chip" to convert existing PATA designs for use with the SATA interface.  Bridged drives have a SATA connector, may include either or both kinds of power connectors, and, in general, perform identically to their PATA equivalents. Most lack support for some SATA-specific features such as NCQ. Native SATA products quickly eclipsed bridged products with the introduction of the second generation of SATA drives.

As of April 2010 the fastest 10,000 RPM SATA mechanical hard disk drives could transfer data at maximum (not average) rates of up to 157 MB/s, which is beyond the capabilities of the older PATA/133 specification and also exceeds a SATA 1.5 Gbit/s link.

SATA revision 2.0 (SATA 3 Gbit/s)

Second generation SATA interfaces running at 3.0 Gbit/s shipped in high volume by 2010, and were prevalent in all SATA disk drives and most PC and server chipsets. With a native transfer rate of 3.0 Gbit/s, and taking 8b/10b encoding into account, the maximum uncoded transfer rate is 2.4 Gbit/s (300 MB/s). The theoretical burst throughput of SATA 3.0 Gbit/s is roughly double that of SATA revision 1.

All SATA data cables meeting the SATA spec are rated for 3.0 Gbit/s and will handle current mechanical drives without any loss of sustained and burst data transfer performance. However, high-performance flash drives are approaching the SATA 3 Gbit/s transfer rate; this is addressed with the SATA 6 Gbit/s interoperability standard.

SATA revision 3.0 (SATA 6 Gbit/s)

Serial ATA International Organization presented the draft specification of SATA 6 Gbit/s physical layer in July 2008, and ratified its physical layer specification on August 18, 2008.  The full 3.0 standard was released on May 27, 2009.  It provides peak throughput of about 600 MB/s (Megabytes per second) including the protocol overhead (10b/8b coding with 8 bits to one byte). Solid-state drives have already saturated SATA 3 Gbit/s with 285/275 MB/s max read/write speed and 250 MB/s sustained with the Sandforce 1200 and 1500 controller. SandForce SSD controllers released in 2011 have delivered 500 MB/s read/write rates, and ten channels of fast flash can reach well over 500 MB/s with ONFI drives – a move from SATA 3 Gbit/s to SATA 6 Gbit/s allows such devices to work at their full speed. Full performance from Crucial's C300 SSD similarly require SATA 3.0. Standard hard disks cannot transfer data fast enough to require more than 3 Gbit/s. There are claims that they can nevertheless benefit from the later standard as reads from their built-in DRAM cache will be faster across the later interface.  According to Seagate "Cache-efficient desktop applications such as gaming, graphics design and digital video editing can experience immediate incremental performance using a SATA 6Gb/s interface". Drives with bigger, faster caches were introduced to benefit from the faster interface.  However, at least one benchmark shows near-identical hard drive performance of SATA 6 compared to SATA 3.  

The 3.0 specification contains the following changes:

  • 6 Gbit/s for scalable performance
  • Continued compatibility with SAS, including SAS 6 Gbit/s. "A SAS domain may support attachment to and control of unmodified SATA devices connected directly into the SAS domain using the Serial ATA Tunneled Protocol (STP)" from the SATA_Revision_3_0_Gold specification.
  • Isochronous Native Command Queuing (NCQ) streaming command to enable isochronous quality of service data transfers for streaming digital content 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 7 mm optical disk drives for thinner and lighter notebooks.
  • Alignment with the INCITS ATA8-ACS standard.

In general, the enhancements are aimed at improving quality of service for video streaming and high-priority interrupts. In addition, the standard continues to support distances up to one meter. The newer speeds may require higher power consumption for supporting chips, although improved process technologies and power management techniques may mitigate this. The later specification can use existing SATA cables and connectors, although it was reported in 2008 that some OEMs were expected to upgrade host connectors for the higher speeds.  

The later standard is backwards compatible with SATA 3 Gbit/s.