What exactly is eSATA?

eSATA means external SATA. Although both eSATA and SATA are serial ATA data transmission lines; the two are not interconnectable:

From Wikipedia:

“eSATA, standardized in 2004, provides a variant of SATA meant for external connectivity. It has revised electrical requirements in addition to incompatible cables and connectors:

• Minimum transmit potential increased: Range is 500–600 mV instead of 400–600 mV.
• Minimum receive potential decreased: Range is 240–600 mV instead of 325–600 mV.
• Identical protocol and logical signalling (link/transport-layer and above), allowing native SATA devices to be deployed in external enclosures with minimal modification
• Maximum cable length of 2 metres (6.6 ft) (USB and FireWire allow longer distances.)
• The external cable connector equates to a shielded version of the connector specified in SATA 1.0a with these basic differences:
  • The external connector has no "L" shaped key, and the guide features are vertically offset and reduced in size. This prevents the use of unshielded internal cables in external applications and vice-versa.
  • To prevent ESD damage, the design increased insertion depth from 5 mm to 6.6 mm and the contacts are mounted farther back in both the receptacle and plug.
  • To provide EMI protection and meet FCC and CE emission requirements, the cable has an extra layer of shielding, and the connectors have metal contact-points.
  • The connector shield has springs as retention features built in on both the top and bottom surfaces.
  • The external connector and cable have a design-life of over five thousand insertions and removals, while the internal connector is only specified to withstand fifty.”

Some of the recent motherboards have an eSATA port attached; however a lot don’t. In fact USB and FireWire are a lot more common than eSATA. This is partly because USB and FireWire actually carry power, whereas eSATA does not.

USB 2 can carry a 5 volt supply at a power rating of 2.5 watts. (1/2 amp (500mA))

USB 3 can carry a 5 volt supply at a power rating of 4.5 watts. (0.9 amp (900mA))

FireWire can carry a supply voltage of 12-25 volts at 15 watts. ( 600 to 800mA )

eSATA carries data only at a voltage of around 500 to 600mV. (Approx. 1/2 volt)

Most computers around at the time of writing don’t have an eSATA port. (Unless one has been fitted after purchase.)

What do you do, then, if you need to use an eSATA-connected device, but your computer doesn’t have an eSATA port?

Answer = You fit an eSATA port.

A lot of PCI or PCIe RAID-controller cards have (an) eSATA port(s) attached to them. While you may not want to use the card for the primary purpose of running an extra RAID array from it, the eSATA port can still be utilised nevertheless.

For instruction in fitting a PCI or PCIe card; see here and here.