Wikipedia ref External SATA on the SATA page.
Identical protocol and logical signaling (link/transport-layer and above), allowing native SATA devices to be deployed in external enclosures with minimal modification
The final eSATA specification features a specific connector designed for rough handling, similar to the regular SATA connector, but with reinforcements in both the male and female sides, inspired by the USB connector. eSATA resists inadvertent unplugging, and can withstand yanking or wiggling which would break a male SATA connector (the hard-drive or host adapter, usually fitted inside the computer). With an eSATA connector, considerably more force is needed to damage the connector, and if it does break it is likely to be the female side, on the cable itself, which is relatively easy to replace.
At the WiserGeek eSATA page
For desktop motherboards that don’t have an eSATA connector, a peripheral component interconnect (PCI) card can be purchased and installed in an available PCI slot that will provide an eSATA interface.
When purchasing an eSATA controller or bus card, be sure it supports the SATA standard required by your SATA hard drive(s). 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.