1

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?

  • You don't specify which versions of Thunderbolt your comparing to which version of USB 3.1 – Ramhound May 24 '17 at 2:27
  • @Ramhound I specified Thunderbolt 3, and there is only one version of USB 3.1. Some people say "gen 1" and "gen 2", but really "gen 1" is just an incorrect name for USB 3.0 over Type C. – brendon-ai May 27 '17 at 23:39
  • There are multiple generations of both standards that's why I asked my question.... – Ramhound May 27 '17 at 23:39
5

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.

  • As for the reason Thunderbolt and USB 3.1 can both use the same Type-C connector that's the beauty of the design. As Ali correctly points out, USB 3.1 is only going to use one of the pairs, while Thunderbolt will use both. It's one of the reason Apple/Intel choose Type-C to base their designs off on – Ramhound May 24 '17 at 3:14
  • Then why the hell doesn't USB 3.1 use both pairs? @Ramhound – brendon-ai May 24 '17 at 12:15
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    @Ethcad, USB3 doesn't use both pairs because it would require twice of transceivers and four extra wires in the cable, which is already thick, stiff, and barely usable and expensive. – Ale..chenski May 24 '17 at 16:39
  • @AliChen I see... That is unfortunate. I wish they would make a "USB 3.2" standard that had the thicker cable and was as fast as Thunderbolt, so then it could be used on phones, tablets, and other ARM devices not blessed by Intel. – brendon-ai May 24 '17 at 19:25
  • @AliChen Ninja'd! Intel just announced today that they are going to be licensing out the Thunderbolt technology royalty free to third-party chip makers. That is excellent news! – brendon-ai May 24 '17 at 19:31
4

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).
  • Thank you for explaining why it is 4x faster instead of just 2x. – brendon-ai May 27 '17 at 23:30

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