External SATA, a special cable and connector used when a SATA (Serial Advanced Technology Attachment) device, usually a hard drive, is housed in an external enclosure. An eSATA connector differs slightly from a standard SATA connector in its use of a key shape to ensure connector and cable alignment, as well as the addition of a shield in both the cable and connector to prevent the pickup of extraneous noise via the eSATA cable.
eSATA is becoming a popular interconnection system for external devices. It allows external devices, usually hard drives, to connect directly to a host (your computer) without the need for any bridging electronics to change protocols, as is necessary with FireWire or USB-based external enclosures.
eSATA external enclosures are usually less expensive than the popular USB-based external hard drives.