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86 points by gwerbret 3 hours ago | 26 comments

DHowett 31 minutes ago

Excellent article.

If I could offer one correction, it would be that SBU (as specified by the USB 3.0 Promoter Group[1]) means "Sideband Use" rather than "Secondary Bus".

On some devices, it is used to carry UART; on others, audio.

[1]: https://www.usb.org/sites/default/files/USB%20Type-C%20Spec%... (pdf)

1a527dd5 11 minutes ago

Tangent: Author has this fabulous post I'd highly recommend: https://fabiensanglard.net/mjolnir/index.html

I read it once years ago and I come back to it every now and then wishing my current PC (10+ years and going) would gently die so I could finally build something small and tiny.

conception 5 minutes ago

This article is why I replaced all the usb dock cables in the office to make sure the usb cable connected to the laptops was transferring enough power so the laptop wouldn't silently lower its frequency for the lower power draw. 10-30% speed bump just because.

retired 6 minutes ago

The simplicity of Thunderbolt. Versions 1 and 2 used mini DisplayPort, 3 and upwards USB-C. Version 1 was 10Gbps, 2 was 20Gbps, 3 was 40Gbps, 4 was 40Gbps, 5 is 80 or 120Gbps with boosting.

A Thunderbolt 5 cable will always support 80Gbps, DisplayPort 2.1, PCIe, USB4 and power of up to 240 watt.

A USB 3 cable? No clue what that cable is capable of.

drob518 4 minutes ago

I’ve been a tech guy for 45 years and I still can’t figure out USB and Thunderbolt and what goes with what and how fast it’s supposed to run.

Neywiny 46 minutes ago

I actually like the 3.2 naming. Gen is speed, "by" is width. It puts it very roughly on par with PCIe's naming which nobody complains about. I just don't like that USB 3, USB 3.1, and USB 3.2 are the same things. And that sales people don't seem to understand that saying a chip supports 3.1 or 3.2 tells me it's anywhere from 5-20gbps which isn't ideal.

retired 3 minutes ago

And not only the sales people. Windows doesn't report anywhere what your motherboard is capable of, and even if you connect with a device it will not tell you the speed it agreed on.

mistyvales 37 minutes ago

PCI-E has had the same standard since its inception: 1.0, 2.0, 3.0, etc. USB has changed multiple times and has remained confusing for the vast majority of people. What was 3.0 is now not 3.0. Even 3.1 has changed. There is no reason to use this naming convention they currently have but for some reason they stick with it..

kimixa 21 minutes ago

PCIe also had things like "1.1", "2.1" and "3.1" - that fixed issues and added functionality - but there wasn't the same crossover between "feature sets and spec revisions" and "speeds" we see in USB today.

Neywiny 21 minutes ago

Possibly they stick with it because it's usable (ish) and it was driving everyone up the wall when they'd change it?

15155 50 minutes ago

Good sheet. Worth adding:

- Female vs male crossover naming and pinouts for Type-C connectors

- Actual voltage, modulation and signaling schemes (USB4v2 uses PAM3 11b/7t encoding)

- PD generations and profiles

mschuster91 48 minutes ago

... and the bunch of proprietary voltage schemes like Quickcharge.

maxloh 31 minutes ago

I once heard that the USB naming is misleading by design so that vendors could still sell older generations accessories they had in stock.

The USB-IF just rebrands the old ones to make them sound current.

Imagine the following naming:

  USB 3.0 / USB 3.1 Gen 1 / USB 3.2 Gen 1 -> USB 3 5Gbps
  USB 3.1 / USB 3.1 Gen 2 / USB 3.2 Gen 2 -> USB 3 10Gbps
  USB 3.2 Gen 2x2 -> USB 3 20Gbps

Isn't that much clearer? I think USB 4 is finally going to the right direction.

xzjis 8 minutes ago

Or it could be: 5 Gbps --> USB 3 10 Gbps --> USB 3.1 20 Gbps --> USB 3.2

Higher number = better

kubik369 19 minutes ago

I think this practice is rather blatantly what you say. The same thing with HDMI forum folding HDMI 2.0 into HDMI 2.1. They made the new 2.1 features optional, therefore manufacturers were able to call their 2.0 devices 2.1 without actually supporting the 2.1 features. AMD has been recently doing similar things, releasing “new” generation of mobile processors where half of them are just rebrands of the older generation.

brcmthrowaway 54 minutes ago

Where does TB5 come into all of this?

syhol 7 minutes ago

- Thunderbolt 3 is a superset of USB 3.1

- USB4 is built on Thunderbolt 3's protocol, implementing a subset of its mandatory features

- Thunderbolt 4 is a strict profile of USB4 (all optional features made mandatory)

- USB4 v2 introduced 80 Gbps signaling

- Thunderbolt 5 is a strict profile of USB4 v2 (again, optional features made mandatory)

Neywiny 45 minutes ago

I don't see why it would. Thunderbolt is not a USB standard

aleph_minus_one 29 minutes ago

> Thunderbolt is not a USB standard

Concerning Thunderbolt 3: USB4 is based on the Thunderbolt 3 protocol [1]:

Concerning Thunderbolt 4: "In July 2020 Intel announced Thunderbolt 4 as an implementation of USB4 40 Gbit/s with additional requirements, such as mandatory backward compatibility to Thunderbolt 3 and requirement for smaller notebooks to support being charged over Thunderbolt 4 ports.[14] Publications such as AnandTech described Thunderbolt 4 as "superset of TB3 and USB4" and "able to accept TB4, TB3, USB4, and USB 3/2/1 connections"." [2]

Concerning Thunderbolt 5: Intel considers Thunderbolt 5 as an implementation of USB4 Version 2.0 [3]

[1] https://en.wikipedia.org/w/index.php?title=USB4&oldid=134742...

[2] https://en.wikipedia.org/w/index.php?title=USB4&oldid=134742...

[3] https://en.wikipedia.org/w/index.php?title=USB4&oldid=134742...

Kirby64 38 minutes ago

Thunderbolt 5 and USB4v2 are the same thing now. They both support 80gbps and pcie pass through.

aleph_minus_one 27 minutes ago

> Thunderbolt 5 and USB4v2 are the same thing now. They both support 80gbps and pcie pass through.

Not completely true: Thunderbolt 5 demands some capabilities that are optional for USB4v2.

Kirby64 17 minutes ago

From a protocol/bandwidth level, it’s essentially the same though. Thunderbolt 5 has some more guarantees for power and display, but the data rate of the two is the same.

stevex 36 minutes ago

Doesn't it run over a USB-C shaped wire? If you're trying to understand things that plug into USB-shaped ports it seems at least worth mentioning.

DiabloD3 3 minutes ago

To be fair: You should refer to these as Type-C cables, as they carry things that are not USB protocol.

The sole exception should be made for "charge only" cables, which can, and should, be referred to as "wired for USB 2.0". These cables "shouldn't" exist, but I also don't want to buy a $30 cable just to charge my phone.

stackghost 27 minutes ago

Thunderbolt 5 is basically just PCI Express, power delivery, and DisplayPort over the same cable, which for reasons passing understanding is terminated with a USB-C connector.

I think most of those cables will also support USB the protocol.

naveed125 25 minutes ago

nice work, thanks