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With Locking Capability
6GB Maximum transfer rate
Hot-swap capability
Thinner Cable construction compares with ATA
Locking latch connector guarantees proper connection to device
Locking Latch connector is compatible with non-locking connector

Background:

Serial ATA (SATA) replaces Parallel ATA (PATA, a.k.a. IDE) as the new standard for high speed, reliable data transfer between your computers motherboard and storage drives.  SATA provides faster data transfers, less clutter due to a more compact cable, leading to better in-case air circulation and ability to hot swap connections.

First generation SATA is generally referred to simply as SATA, but is also known as SATA 150 or SATA 1, has a thoughput of 1.5 gbit/s.  It is an internal interface that uses "L" type connectors.  They are referred to as "L" connectors because if you look at the female connector head on, it has a sideways "L" shaped slot.  The male connector has an "L" shaped tongue.

Second generation SATA is known as SATA  3 Gbps but commonly referred to as SATA 2 and sometimes SATA 300.  It supports a 3.0 Gbps transfer rate and also uses the "L" type connector.  SATA 2 cables are backward compatible with first generation SATA devices.  However, maximum throughput will be limited to the least common denominator.

To go with the newer SATA interface, SATA drives usually employ a new 15 pin power connector as oppose to the older 4 pin Molex power connectors used on older system.  However, some drives will have both types of connections for ease of installation into legacy systems.

Here's where it can get confusing.  For use with external devices, eSATA was developed with a completely different type of connector.  eSATA uses "I" (letter i) type connectors because, as before, if you look at the connector straight on, there is an "I" shaped slot or tongue.  Not to be confused with SATA 1 (#1) which some manufacturers will label SATA I (roman numeral i) which tends to confuse some users.  So a cable that is labeled as having type "I" connectors are for eSATA and not SATA 1 cables. 

eSATA has a maximum bandwidth of 6.0 gbit/s, same as SATA 3.  But along with the new connector type, it also calls for a shielded cable.  Though it has a faster transfer speed than USB 2.0 and Firewire 400/800 it has a shorter maximum range of 2 meters.