Serial ATA refers to a type of hard disk drive interface.
SATA stands for serial advanced technology attachment. SATA was introduced in 2002 as the standard for hard disk drives in personal computers. SATA II is the name applied to the newer, faster SATA interface introduced later the same year.
Misnomer
SATA II was not the original name for the newer SATA interface; it was the name of the committee that developed the technology. However, the name has since become associated with the technology itself.
Speed
The original SATA devices have a standard data transfer speed of 1,500 megabits per second. The effective clock speed of the typical SATA device is 150 megabytes per second, therefore, these hard drives are known as SATA-150. SATA II devices feature a higher clock speed of 300 megabytes per second. SATA drives capable of 300 MB/s are known as SATA-300 devices. Not all SATA-300 drives are SATA II. In order to be classified as SATA II, the drive must have Native Command Queuing capabilities.
Native Command Queuing
SATA hard drives handle multiple commands by processing them in the order in which the commands are received. Unfortunately, processing the commands in order is not always the most efficient way to proceed. NCQ, or Native Command Queuing, allows a SATA II drive to re-order commands in order to execute them in the most efficient order possible. NCQ results in improved disk and system performance.
Port Multiplier
The port multiplier feature of SATA II drives allows up to 15 disks to be connected on a single SATA channel. This feature, while introduced as a SATA II component, is backward compatible with SATA devices. However, the slower speed of the SATA drives could potentially lead to problems with connecting multiple devices.
Hot Plug
SATA II devices have "hot plug" capabilities. This means that they can be added and removed without shutting down the system. The earlier SATA devices did not have this capability.
Click Connect and eSATA
The original SATA drives were intended for internal use only. The connections were often loose. SATA II devices have a Click Connect feature, which means you should hear a click when the device is firmly seated. Therefore, SATA II drives can be more securely attached, allowing for external SATA II or eSATA drives to be attached. The eSATA devices can be attached by a cord of up to 2 meters long. More recently, an xSATA specification was added that allows for an external drive to be connected with a cord up to 8 meters long.
Staggered Spin-Up
With the original SATA drives, multiple drives had to be powered up at the same time, causing a severe drain on the system's resources. SATA II drives are capable of staggered spin-up, meaning the devices can be powered up separately, thus avoiding potential system drain.
Link Power Management
SATA II also features Link Power Management, which lets the system power the hard drive in one of three ways: active, partial or slumber state. This power management system allows the computer to conserve power, which is particularly helpful for mobile computing.
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