Q Thunderbolt external disk enclosures seem very expensive. Just how much quicker are they?
A Thunderbolt is a relatively new technology, and largely (but not exclusively) Mac-only. It also requires an Intel controller chip, and complex cables with their own chips. The original Thunderbolt, now numbered 1, offers two channels, each with a maximum data throughput of 10 Gb per second (in practice, around 1 GB per second). Thunderbolt 2, built into more recent Mac models, can link both these into a single channel with double the throughput, 20 Gb per second (around 2 GB per second).
For comparison, eSATA can offer up to 6 Gb per second, USB 3.0 up to 6 Gb per second, USB 2.0 up to 0.48 Gb per second, and FireWire 800 up to 0.8 Gb per second. So you can reasonably expect Thunderbolt 2 to peak at over 20 times the best speed of FireWire 800. To see anything like that difference, the rest of the interface needs to be very quick, and the drive itself must be high performance.
Thunderbolt does, therefore, deliver good value for your money.
Updated from the original, which was first published in MacUser volume 28 issue 15, 2012.