Difference Between SATA II and SATA III

SATA is a hardware connection standard that provides data transfer between hard drives and a computer's motherboard. The current standard is SATA III as of December 2012; SATA I was supplanted by SATA II around 2006. SATA connectors have been the default way of connecting hard drives to motherboards since around 2004 The first SATA hard drives were released in 2003 and had significant performance increases.

Transfer Speeds

The primary difference between SATA II and SATA II is the transfer speed, which is measured in gigabits per second. SATA II has a peak transfer rate of 3 Gbps, SATA III has a peak transfer rate of 6 Gbps. One Gbps is roughly 100 megabytes per second pulled from the drive.

Connectors and Cables

SATA ports on motherboards and the cables that connect hard drives use a different interface than the older IDE standard; this simplified assembling computers, and the cables are both less expensive and more durable. Regardless of the generation of SATA being used, the cables are identical and using an old SATA cable does not impact the data transfer speed.

Compatible Drives and Ports

If an SATA II device is plugged into a SATA III port, the port detects the slower device, and the data transfer rate is dialed down to match. To get maximum performance, always make sure that your hard drive's SATA generation matches the SATA ports on the motherboard of the computer you're building.

Nomenclature Change

In 2010, the standards organization behind SATA broke away from using Roman numerals to designate SATA generations, and lists them by their transfer rates in Gbps. SATA II became SATA -- 3.0 gigabit -- and SATA III became SATA -- 6.0 gigabit.

What is the difference between SATA I, SATA II and SATA III?

SATA I (revision 1.x) interface, formally known as SATA 1.5Gb/s, is the first generation SATA interface running at 1.5 Gb/s. The bandwidth throughput, which is supported by the interface, is up to 150MB/s.

SATA II (revision 2.x) interface, formally known as SATA 3Gb/s, is a second generation SATA interface running at 3.0 Gb/s. The bandwidth throughput, which is supported by the interface, is up to 300MB/s.

SATA III (revision 3.x) interface, formally known as SATA 6Gb/s, is a third generation SATA interface running at 6.0Gb/s. The bandwidth throughput, which is supported by the interface, is up to 600MB/s. This interface is backwards compatible with SATA 3 Gb/s interface.

SATA II specifications provide backward compatibility to function on SATA I ports. SATA III specifications provide backward compatibility to function on SATA I and SATA II ports. However, the maximum speed of the drive will be slower due to the lower speed limitations of the port.

Example: SanDisk Extreme SSD, which supports SATA 6Gb/s interface and when connected to SATA 6Gb/s port, can reach up to 550/520MB/s sequential read and sequential write speed rates respectively. However, when the drive is connected to SATA 3 Gb/s port, it can reach up to 285/275MB/s sequential read and sequential write speed rates respectively.

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Understanding SCSI, ATA, SAS and SATA

For years the parallel interface has been widely used in storage systems. The need for increased bandwidth and flexibility in storage systems made the SCSI and ATA standards an inefficient option. A parallel interface is a channel capable of transferring date in parallel mode — that is transmitting multiple bits simultaneously. Almost all personal computers come with at least one parallel interface. Common parallel interfaces include SCSI and ATA.

SCSI

(sku4ze) Short for small computer system interface, a parallel interface standard used by Apple Macintosh computers, PCs and many UNIX systems for attaching peripheral devices to computers. Nearly all Apple Macintosh computers, excluding only the earliest Macs and the recent iMac, come with a SCSI port for attaching devices such as disk drives and printers. SCSI interfaces provide for data transmission rates (up to 80 megabytes per second). In addition, you can attach multiple devices to a single SCSI port, so that SCSI is really an I/O bus rather than simply an interface.

ATA

(Also known as IDE) is a disk drive implementation that integrates the controller on the disk drive itself. ATA is used to connect hard disk drives, CD-ROM drives and similar peripherals and supports 8/16-bit interface that transfer up to 8.3MB/s for ATA-2 and up to 100MB/s (ATA-6).

So, what do parallel interfaces have to do with SAS (Serial Attached SCSI) and SATA (Serial ATA)? A lot, actually. It is the architectural limitations of the parallel interfaces that serial technologies like SAS and SATA address. In contrast to multiple parallel data stream, data is transmitted serially, that is in a single steam, by wrapping multiple bits into packets and it is able to move that single stream faster than parallel technology.

Serial Attached SCSI (SAS)

Abbreviated as SAS, Serial Attached SCSI, an evolution of parallel SCSI into a point-to-point serial peripheral interface in which controllers are linked directly to disk drives. SAS is a performance improvement over traditional SCSI because SAS enables multiple devices (up to 128) of different sizes and types to be connected simultaneously with thinner and longer cables; its full-duplex signal transmission supports 3.0Gb/s. In addition, SAS drives can be hot-plugged.

Serial ATA (SATA)

Often abbreviated as SATA, Serial ATA is an evolution of the Parallel ATA physical storage interface. Serial ATA is a serial link — a single cable with a minimum of four wires creates a point-to-point connection between devices. Transfer rates for Serial ATA begin at 150MB/s.

Starting with SATA, it extends the capabilities of ATA and offers transfer rates starting at 150MB/s and, after years of development, has moved to the mainstream of disk interfaces. The successor the SCSI interface is SAS at speeds of up to 3Gb/s. Additionally, it also addresses parallel interface issues such as drive addressability and limitations on the number of device per port connection.

SAS devices can communicate with both SATA and SCSI devices (the backplanes of SAS devices are identical to SATA devices). A key difference between SCSI and SAS devices is the addition in SAS devices of two data ports, each of which resides in a different SAS domain. This enables complete failover redundancy. If one path fails, there is still communication along a separate and independent path.

Cables & Connectors

Another big advantage of SATA over ATA is the cabling and connectors. The serial interface reduces the amount of wires needed to transmit data, making for much smaller cable size and making it easier to route and install SATA devices. The IDE cables used in parallel ATA systems are bulkier than Serial ATA cables and can only extend to 40cm long, while Serial ATA cables can extend up to one meter. In addition to the cabling, a new design of connectors is also used that reduces the amount of crosstalk between the wires, and the connector design also provides easier routing and better air flow.

The Benefits of SAS & SATA in Storage

Serial interfaces offer an improvement over older parallel SCSI (with a serial version) in storage applications and environments. These benefits include better performance, better scalability, and also better reliability as the parallel interfaces are at their limits of speed with reliable data transfers. SAS and SATA drives can also operate in the same environment while SCSI and ATA cannot. For example, using faster SAS drives for primary storage and offloading older data to cheaper SATA disks in the same subsystem, something that could not be achieved with SCSI and ATA.

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