The Intel white paper on Thunderbolt says: Furthermore, the website Anandtech notes: In addition, Apple says the following on their Thunderbolt website (my emphasis on the two channels): Thus, if you believe all of the above there should be a total of 20Gbps of output (or input) on the MacBook's single Thunderbolt port. However, all of the marketing materials for the new MacBook Pros simply state "data transfer rates up to 10 Gbps." Thus, my question would be, since it appears that one channel can transfer up to 10Gbps what happened to the second channel's 10Gbps? The simply explanation would be that a single device can be served by only one channel (i.e. the channels can't be bonded, which makes some sense), and thus when Apple says "data transfer rates up to 10Gbps" they are talking about i/o to a single device. But if that is the case, why don't they mention that in a daisy-chain a second device can also receive up to 10Gbps by using the second channel? Intel's white paper seems to hint at that possibility: Intel also says: So, what is it? Does the MacBook's Thunderbolt port provide a total maximum of 20Gbps input and 20Gbps out, or does it only provide a total of 10Gbps in each direction? I think I may have an answer (but it could be a bit controversial), so I wanted to pose this question to see if anyone had a good explanation as to why the numbers don't seem to add up.