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As I understand it, Thunderbolt 3 and USB 3.1 use the exact same USB-C connectors. I am aware that Thunderbolt 3 is approximately quadruple the speed of USB 3.1. I had assumed that it was because TB ran on optical fiber, but apparently this is not true, according to https://en.wikipedia.org/wiki/Thunderbolt_(interface). I also know it's not a parallel interface.

In that case, why is TB3 faster than USB 3.1? Is it something to do with the controller, or the cable itself?

brendon-ai
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2 Answers2

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TB is faster because it uses TWO pairs of Rx/Tx lanes, while USB 3.0/3.1 uses only one pair. USB 3.1 cables contain only one set of differential Rx/Tx pairs, while TB uses two pairs, and therefore is thicker and more expensive.

In Type-C connector, USB 3.1 uses only one set of Rx/Tx contacts, or another set, depending on which way a cable is plugged in. And a USB 3.1 host uses data multiplexer to switch to corresponding pin set. The TB uses BOTH sets of high-speed data pairs.

For the same (comparable generation) transceiver technology, 5Gb, 10Gb, whatever, the TB will be always ~2X faster, since its data path is 2x wider.

Ale..chenski
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Thunderbolt 3 is up to 4x as fast as USB 3.1 Gen 2 (SuperSpeed+, 10Gbps) for two reasons:

  1. It uses both of the high speed pairs-of-pairs in the Type C cables.
  2. Thunderbolt 3's 40Gbps mode uses faster signaling over at least one of those pairs, but to make that faster signaling work, it took a tough trade-off of limiting it to only ≤ 0.5m passive cables, or expensive 2m active cables (cables with special IC chips in the connectors to assist in signal handling).
Spiff
  • 110,156