Serial ATA, also known as SATA, is a computer interface that supports SATA hard drives and optical drives. Serial ATA was created to replace IDE, which can be called Parallel ATA. It uses just 7 pins as opposed to 40 that were used by IDE devices. SATA devices communicate with a SATA host adapter using just 4 conductors. The other 3 pins are used for ground. To make serial ATA backwards compatible with ATA, SATA uses many of the same commands as legacy devices.
Serial ATA hard drives boast a much faster transfer speed than traditional ATA hard drives. Even the slowest SATA connection, SATA revision 1.0, is faster than the fastest PATA connection. The fastest SATA connection, SATA revision 3.0, is about 6 times faster than PATA. This makes transferring large files to and from your hard drive extremely fast.
The best thing about SATA hard drives is that they are hot-pluggable. The specifications for SATA include hot plugging of devices, and any host adapter or device meeting these specifications will be able to be disconnected and reconnected from a computer without turning off the power. This allows you to replace a SATA hard drive that has failed without ever rebooting your computer. This makes SATA hard drives a great choice for a RAID configuration (Redundant Array of Inexpensive Disks).
The standard conformed to by external devices is known as eSATA and was standardized in 2004. This specification provides a variant of SATA which can be used for external devices such as SATA hard drives, DVD drives and more. Most USB and FireWire drives use SATA hard drives along with a controller that converts the signal from SATA to USB or FireWire. This conversion causes some inefficiency which makes native SATA hard drives using an eSATA much faster than an external USB or FireWire hard drive.