Other SATA specs
Given the different versions of SATA and features that can, but aren't always used, knowing exactly what you're getting can be confusing. Hopefully we can clear some of that up here.
The majority of early SATA hard drives are quite simply PATA drives featuring a bridge to convert them to SATA connectivity. The system may be communicating with one side of the bridge at 1.5Gbps, but the rest of the drive's controller may be limited by its PATA technology. Other drives are designed as SATA drives, rather than being made compatible through a bridge. This native approach allows for higher potential performance. If you're purchasing a SATA drive and performance is important to you, then you should be on the lookout for native drives.
SATA II is a term you may run into and is often associated with a newer version of SATA. However, it was infact the name of the group in charge of developing the SATA specification. They are now called the SATA-IO. The table below is taken from the official webpage of SATA-IO, outlining some of various features that can be supported by SATA drives and associated equipment.
The current SATA standard is version 1.0a. However, there are features that exist as an extension to this. They do not have to be implemented and any extensions are designed to be backwards compatible, but they can be used where manufacturers see fit.
NCQ is one of the capabilities which can be included in SATA drives. It allows a queue of requests to be organised to allow data transactions to occur more efficiently, rather than dealing with each request one at a time. NCQ is shown below, the image courtesy of www.nvidia.com. It is clear from the diagram that a drive with NCQ enabled is much more efficient at accessing data than a drive without the technology.
For systems with many SATA disks, perhaps in a RAID array, staggered spin-up is an appealing feature, in that each drive has its spin-up deferred for a short period, allowing the drives to start without putting a large load on the system's power supply.
The newest SATA chipsets support 3Gbps transfer rates, doubling the original transfer rate. NVIDIA's nForce 4 is an example of a chipset which features 3Gbps SATA channels. You will also need 3Gbps capable drives to make use of this feature, however.
Some users have complained about the durability of SATA cables and their ability to come loose. This has been rectified with a new 'ClickConnect' plug, which has a spring clip and clicks into place when plugged in.
The list of features goes on, including external SATA, hot plugging, cache bypassing and more. You will find these features implemented by manufacturers depending on the intended use and target market of the product.