The brains behind the port you'd find on one computer would be similar to the same port on another machine, right? That's not the case when it comes to the Thunderbolt ports on the latest MacBook Airs, whichclub earlier this month.
A report on AnandTech notes that the Thunderbolt controller found on the MacBook Air is a smaller version than the ones found on other Thunderbolt-equipped Macs so far. With other machines, Apple's been using a controller code-named Light Ridge that sports four, bidirectional Thunderbolt channels and two DisplayPort outputs. However the 11.6-inch and 13.3-inch models of the Air sport a controller code-named Eagle Ridge, that drop it down to two bidirectional channels and one DisplayPort output.
Why the difference? The Eagle Ridge chip's designed for machines without discrete graphics, which includes the new Airs. In the move to Intel's Sandy Bridge chipset, the Airs dropped the dedicated NVIDIA GeForce 320M GPU in favor of Intel's HD Graphics 3000 processor, which is built right into the CPU. That means the Air is still capable of supporting an external screen, but not two as Apple's 15- and 17-inch MacBook Pro models are able to do, hence needing only one DisplayPort output. The speed you'd get from either chip remains as advertised, with two bidirectional channels for data, while Apple gets to save some space--and as AnandTech notes--likely money on the part.
One of the internal differences with the Airs that's worth paying attention to is the built-in storage speed between the models. Earlier this week, differences in the read/write speeds of the 128GB SSD drives were found in the 11.6- and 13.3-inch models of the Air, with the 13.3-inch model posting lower scores in a handful of tests from both Engadget and TLD Today. Apple continues to make that part unofficially user-replaceable by not soldering it to the motherboard.