External Serial Advanced Technology Attachment or eSATA is an external interface for SATA technologies. It competes with FireWire 400 and universal serial bus (USB) 2.0 to provide fast data transfer speeds for external storage devices.

SATA replaced ATA legacy technology as the next generation internal bus interface for hard drives. The SATA interface is more streamlined than ATA and provides serial architecture for greater speed than the older parallel technology. SATA cables are narrow and can be up to three feet (1 meter) in length, whereas parallel cables are much wider and limited to a length of 18 inches (45.7 cm). With eSATA, the speed of SATA expands to encompass exterior storage solutions.

While eSATA reaches transfer rates triple those of USB 2.0 and FireWire 400, it does have one drawback. eSATA requires its own power connector, unlike the aforementioned interfaces. However, it is an excellent choice for external disk storage. Unlike USB and FireWire interfaces, eSATA does not have to translate data between the interface and the computer. This enhances data transfer speeds, while saving computer processor resources and eliminating the need for an extra off-load chip.

For desktop motherboards that don’t have an eSATA connector, a bus card can provide an eSATA interface. Notebooks can use a peripheral component interconnect (PCI) card. eSATA enables use of fast SATA drives for external disk arrays, not only expanding valuable storage real estate, but also enabling truly fast portable storage. eSATA's hot-swappable feature makes taking disks from work to home, or from one computer to another, a snap. Administrators, IT techs, advertising and marketing executives, and even gamers will find this beneficial.

SATA has differing standards, with older hardware supporting the original standard exclusively. With each new SATA iteration, speed increases. Original SATA, or SATA/150, has a data transfer speed of 150 megabytes per second (MB/s). SATA II or SATA/3Gbs doubled the speed to 300 MB/s or 3 gigabits per second. This is also sometimes referred to as SATA/300. Some sources report SATA/600 will be available by 2007.

When purchasing an eSATA controller or bus card, be sure it supports the SATA standard required by your SATA hard drive(s). Hardware that supports newer standards is usually backwards compatible with older devices, but the reverse does not hold. An eSATA controller made for SATA/150, for example, will not be able to support the faster transfer speeds of a SATA/300 hard drive.