Understanding eSATA

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eSATA



Standardized in 2004, eSATA (e=external) 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 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, whereas the internal connector is specified to withstand only 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,[7] about four times the maximum transfer rate of USB 2.0 or FireWire 400 (IEEE 1394a) and almost twice as fast as 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 some USB [1] or FireWire or USB+FireWire bridges. eSATA does not suffer from these issues provided that the controller manufacturer (and its drivers) presents eSATA drives as ATA devices, rather than as "SCSI" devices (as has been common with Silicon Image, JMicron, and NVIDIA nForce drivers for Windows Vista); In those cases, even SATA drives will not have low-level features accessible. USB 3.0's 4.8 Gbit/s and Firewire's future 6.4Gb/s (768 MB/s) will be faster than eSATA I, but the eSATA version of SATA 6G will operate at 6.0Gb/s (the term SATA III is being eschewed by the SATA-IO to avoid confusion with SATA II 3.0 Gb/s, which was colloquially referred to as "SATA 3G" [bps] or "SATA 300" [MB/s] since 1.5 Gb/s SATA I and 1.5 Gb/s SATA II were referred to as both "SATA 1.5G" [b/s] or "SATA 150" [MB/s]). Therefore, they will operate at negligible differences of each other [15].


HDMI, Ethernet, and eSATA ports on a Sky+ HD Digibox, which allows for extended external DVR storage.
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.[16]

Prior to the final eSATA 6 Gb/s specification many add-on cards and some motherboards advertise eSATA 6 Gb/s support because they have 6 Gb/s SATA 3.0 controllers for internal-only solutions. Those implementations are non standard and eSATA 6 Gb/s requirements will be ratified in the upcoming SATA 3.1 specification.[3] These products might not be eSATA 6 Gb/s compliant.

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[MasterZuFu]

Again, copy and pasted without giving proper credits to the original source.

http://en.wikipedia.org/wiki/Esata#eSATA