> is there a difference between elbow SATA connectors and the ones with identical straight ends?
Depends on what you mean:
For the SATA connectors that attach to hard drives,
there are right-angle, left-angle and straight connectors.
The right- and left-angle connectors are highly recommended
because they tend to stay put while inserting one's hand(s)
into a case, e.g. for routine maintenance, upgrades,
If you bump the straight-line connectors, the resulting torque
on the cables may cause the connector to mis-align or even break
the housing on the hard drive: I have seen instances
of the latter damage.
If you mean the difference between the I-connector and L-connector
at the other end of a SATA cable, the latter is for standard SATA connections
and the former is for eSATA aka external Serial ATA connections.
The eSATA connector was designed for cables that carry a slightly
higher voltage, so that eSATA cables can extend longer than
internal SATA cables.
Also, good eSATA connectors should have a metal shield
on the connector housing, which is designed to
discharge any static buildup before the signal pins connect:
this facilitates "hot-swapped" external enclosures -- much like
USB connectors which can be inserted and removed while
the system is running.