Thunderbolt Cable Teardown Reveals Electronics and Firmware
A source within the telecom industry explained to Ars that active cables are commonly used at data rates above 5Gbps. These cables contain tiny chips at either end that are calibrated to the attenuation and dispersion properties of the wire between them. Compensating for these properties "greatly improves the signal-to-noise ratio" for high-bandwidth data transmission.
iFixIt tore down the new ThunderBolt cable and found two Gennum GN2033 chips in the connector, one on each side. Additional support chips and resistors were also found for total of 12 chips and "tons" of smaller electronic components.
Gennum's chip is described as a transceiver that enables "reliable data transfer at cutting-edge speeds over low cost, thin-gauge copper cables." Early benchmarks of Thunderbolt drive enclosures show massive improvements over FireWire 800.
One interesting benefit of this "active" cabling is that current Thunderbolt ports found in the iMac and MacBook Pro will be future-compatible with planned optical Thunderbolt cables. Optical cables were part of the original plans for Thunderbolt which promises to offer much higher speeds, but the first version released are based on traditional copper wiring. Intel still plans on upgrading to optical cabling in the future, and existing Thunderbolt devices should be compatible with new cabling. This was mentioned during the original Thunderbolt roll out.
...the port you'll find in new MacBook Pros and storage devices can actually take an optical cable when those are cost-effective enough to roll out, because Intel will eventually bake the optical transceivers into the cables themselves.
Ars, however, suggests that the high cost and complexity of the cabling may be a hurdle to widespread adoption of Thunderbolt.