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1. Definition. What is SATA?
2. SATA Timeline
3. SATA Specifications
4. SATA Modes
5. SATA Speeds
6. SATA Cabling
7. External SATA (eSATA)
8. Deep Dive SATA Study

Definition: What is SATA?

As of 2011, SATA or Serial AT Attachment interface, is the connection used by modern computers to attach mass storage devices such as hard drives, to the computer. SATA has replaced PATA as the de-facto standard for hard drive busses, and differs from PATA in that it transmits 1 bit at a time, but at very high speeds. SATA was delveloped to overcome the difficulties with electromagnetic interference and signal timing experienced by existing Parallel ATA (PATA).

The biggest difference between Serial ATA and Parallel ATA is that SATA sends 1 binary bit at a time, compared to the 40 pin 16-bit data transport of PATA IDE architecture. However, PATA runs at a maximum of 133Mhz transferring 16 bits per cycle, and SATA runs at 1.5 Ghz (1500 Mhz) at 1 bit per cycle.

SATA Timeline

• SATA 1.0 Specification (DRAFT) - November 2000
• SATA 1.0 Specification - August 2001
• SATA II Extensions
• SATA 2.0 Specification (April 2004)
• SATA 2.5 Specification (August 2005)
• SATA 2.6 Specification (March 2007)
• SATA 3.0 Specification (2009)
• SATA 3.1 Specification (July 2011)

SATA Specifications & Standards

SATA 1.0 (SATA-150)

The draft specification was delivered at the Intel Developer Forum in November 2000 and outlined a new serial communications scheme for data transport and signalling large storage devices (disk drives). The draft specificaiton outlined a 1.5 Ghz bus speed with 1 bit per cycle enabling data transfer and signalling at speeds up to 1.5 Gbps (roughly 150 MBps). The SATA 1.0 specification finalized in August 2001. SATA versions are often referred to by the speed of the transport in megabytes per second (SATA-150).

SATA II Extensions

The SATA II extensions added network support enabling network storage vendors to utilize this newer high speed technology.

SATA 2.0 (SATA-300)

The SATA 2.0 Specification was released some time in April 2004 and increased the clock speed of the SATA bus to 3Ghz. This increased throughput on the bus to 3 gigabit (Gb) per second or roughly 300MB per second and is often referred to as SATA-300.

SATA 2.5

The SATA 2.5 specification was released in August 2005. The SATA 2.5 specification added Native Command Queuing (NCQ), eSATA support along with hot-plugability support, the port multiplier and staggered spin-up. Much of these functions benefit network based storage appliances, but are available on some servers and desktop computers.

Native Command Queuing (NCQ)

New in SATA 2.5, Native Command Queuing is a design feature that is internal to the Serial AT interface which improves SATA performance under load. Both the drive and the controller must support it. As the ttransactional workload increases on SATA based drives, Native Command Queuing (NCQ) improves the performance and reliability, grouping reads and writes together in the order of processing processing efficiency to reduce the workload of the mechanical parts, reduce seek time, reduce latency and improve the overall speed of data transfer from the physical surface of the drive. NCQ is backwards compatible with non-NCQ SATA versions, and is available on any computer system where the drives support NCQ and the SATA version supports it, including desktop computers. Speed improvements of 8-12% over non-NCQ systems is common.

Hot Plugability and eSATA

Hot pluggability, the ability to remove a drive while the computer is still running, was added partly to support the Network Storage Appliance vendors who needed their the speed provided by SATA, but also needed the convenience of being able to remove and replace drives without shutting down the system. Along with this hot plugability was added an external SATA function to allow drives to be connected externally to computer systems.

Port Multiplier

Port multipliers allow a single SATA controller port to communicate with multiple SATA-compatible devices (drives) which increases the scalability of SATA and lowers the cost of the hardware by reducing the need for additional controllers. The port multiplier functionality is transparent to drive operation. Controllers supporting SATA port multipliers must also support Frame Information Structure (FIS) based switching or command-based switching.

Staggered Spin-Up

Normally, when you turn on the computer, everything in the computer turns on. When the controller and the drive support SATA staggered spin-up, the startup of each of the drives is staggered in order to reduce the peak electrical load placed on the power supply.

SATA 2.6

The SATA 2.6 specification was released in March 2007. SATA 2.6 added support for micro and slimline SATA cables.

SATA 3.0 (SATA-600)

The SATA 3.0 specification was released in 2009. SATA 3.0 increased the bus speed yet again to 3Ghz, which at 1 bit per hertz allows up to 3Gb per second or roughly 600MB per second throughput. Real-world throughput tends to peak at 580MB/sec.

SATA 3.1 (SATA Express)

The SATA 3.1 specification was released in August of 2011. The specification aims at utilizing the higher-speed PCI bus technology, specifically the PCIe 3.0 specification, to achive up to 16Gbps transfer speeds to and from disk to support high-speed Solid State Disk Drives (SSDD) which have higher throughput and transaction rates than standard physical spindle-platter electromagneto drives.

SATA 3.1 adds the several features supporting low-power and mobile devices:

• Universal Storage Module (USM™): USM enables developers to incorporate slots into their consumer electronics devices that accept powered, cable-free storage modules with an integrated SATA interface, offering portable, scalable storage solutions
• mSATA – SATA for mobile computing devices, now with enhanced auto detection to provide increased interoperability by eliminating the need for a dedicated mSATA connector
• Zero-Power Optical Disk Drive (ODD) – eliminates the power consumption of an idle SATA ODD, resulting in increased energy savings
• Required Link Power Management – drives energy efficient power management across all SATA devices, reducing overall system power demand
• Queued Trim Command – allows SATA SSDs to execute Trim without impacting normal operation, improving SSD performance
• Hardware Control Features – enable host identification of device capabilities, allowing hosts to make more effective use of SATA device

SATA Modes

• Legacy
• AHCI
• RAID

Legacy Mode

Legacy mode was created to allow SATA to remain compatible with existing Parallel ATA (PATA) components. SATA supports all the legacy PATA commands

AHCI

RAID

SATA Speeds

SATA Cabling