As noted by Arstechnica and iFixIt, Apple's new $50 Thunderbolt cable is actually a "smart" or "active" cable that contains circuitry and firmware. Arstechnica explains:
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.
Top Rated Comments
Keep in mind, Thunderbolt is two 10Gbps channels. Let's face it -- 20Gbps aggregate bandwidth is a LOT of bandwidth for an external cable which is getting up there in numbers to rival the amount of memory bandwidth most commodity computer chipsets have (I think two-channel X68 is 21.6Gbps), and those chipsets aren't exactly dirt cheap. This is bandwidth normally the realm of single mode fiber optics for cabling, and even then, the equipment on either side of that single mode cable isn't cheap.
This is not a dumb piece of shielded wire. This is a PCI-E breakout.
This is why the first thunderbolt peripherals are DAS RAID arrays and FCAL HBAs. This is stuff really intended for the professional market at the moment, not consumer devices, as there isn't a consumer device need for this crazy (yes, it's crazy!) amount of bandwidth. Not until production significantly catches up will things start to become cheap enough to make consumer devices.
This is why Apple is pushing Thunderbolt. Even in it's first incarnation it is an insane amount of overkill. It will not be quickly obsolesced.
Too funny.:)
Why couldn't apple just put those chips in the computer themselves.
My gut feeling was so they have an excuse to charge an arm and a leg for the cables.
Because the chips help with handling attenuation on the cable, and it's part of the Thunderbolt spec. Without the chips, reaching 20Gbps over copper is incredibly hard.
PS: Read http://news.ycombinator.com/item?id=2711918 for a better understanding.