eSATA
| External Serial ATA (SATA)/Universal Serial Bus (USB) with Power | |
 eSATA-USB | |
| Year created | 2008 |
|---|---|
| Speed | SATA Rev. 1: 1.5 Gbit/s, SATA Rev. 2: 3 Gbit/s, SATA Rev. 3: 6 Gbit/s, USB High Speed: 480 Mbit/s, USB SuperSpeed: 5 Gbit/s |
| Style | Serial |
| Hotplugging interface | Yes |
| External interface | eSATAp, eSATA, USB, eSATApd |
External SATA (eSATA) is a variant of the Serial ATA (SATA) interface designed for connecting external storage devices to a computer. Standardized in 2004 by the Serial ATA International Organization, eSATA defines connectors and cables electrically distinct from internal SATA in order to make the two physically incompatible and to meet the more demanding requirements of external use. It was widely adopted on desktop computers, laptops, and external hard-drive enclosures during the late 2000s before being largely displaced by USB 3.0 and, later, USB-C and Thunderbolt interfaces.
- 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 signaling (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.
Aimed at the consumer market, eSATA enters an external storage market already served by the USB and FireWire interfaces. Most external hard-disk-drive cases with FireWire or USB interfaces use either PATA or SATA drives and "bridges" to translate between the drives' interfaces and the enclosures' external ports, and this bridging incurs some inefficiency. Some single disks can transfer 131 MB/s during real use, more than twice the maximum transfer rate of USB 2.0 or FireWire 400 (IEEE 1394a) and well in excess of the maximum transfer rate of FireWire 800, though the S3200 FireWire 1394b spec reaches ~400 MB/s (3.2 Gbit/s). Finally, some low-level drive features, such as S.M.A.R.T., may not operate through USB or FireWire bridging. eSATA does not suffer from these issues. USB 3.0's 5.0 Gbit/s and Firewire's future 6.4 Gbit/s will be faster than eSATA I, but the eSATA version of SATA III will operate at 6.0 Gbit/s, thereby operating at negligible differences of each other.
eSATA can be differentiated from USB 2.0 and FireWire external storage for several reasons. As of early 2008, the vast majority of mass-market computers have USB ports and many computers and consumer electronic appliances have FireWire ports, but few devices have external SATA connectors. For small form-factor devices (such as external 2.5-inch disks), a PC-hosted USB or FireWire link supplies sufficient power to operate the device. Where a PC-hosted port is concerned, eSATA connectors cannot supply power, and would therefore be more cumbersome to use.
Owners of desktop computers that lack a built-in eSATA interface can upgrade them with the installation of an eSATA host bus adapter (HBA), while notebooks can be upgraded with Cardbus or ExpressCard versions of an eSATA HBA. With passive adapters the maximum cable length is reduced to 1 metre (3.3 ft) due to the absence of compliant eSATA signal-levels. Full SATA speed for external disks (115 MB/s) have been measured with external RAID enclosures.
eSATA may attract the enterprise and server market, which has already standardized on the Serial Attached SCSI (SAS) interface, because of its hotplug capability and low price.
Prior to the final eSATA specification, a number of products existed designed for external connections of SATA drives. Some of these use the internal SATA connector or even connectors designed for other interface specifications, such as FireWire. These products are not eSATA compliant. 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.