USB Cheat Sheet (2022)
fabiensanglard.net227 points by gwerbret 8 hours ago
227 points by gwerbret 8 hours 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)
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.
You know, accidents happen. If you were to trip over the carpet and that venerable PC falls in the dumpster.
I don't know what short-distance data communications will be like in 2050, but we know it will be called USB.
USB-G 4.6 SuperSpeed Plus, but the cables will still just be used for charging your random electronics and won't even work for that half the time.
I know not with what technology 2030 will use, but 2040 will use USB sticks and stones.
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.
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..
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.
Manufacturers of mainstream consumer motherboards never used 1.1, 2.1, etc. for PCI-E though. What is 4.0 on the spec sheet will be 4.0 to the buyer. My old 2016 motherboard has a slew of 3.0 labelled USB ports that are now not 3.0, hence the conundrum. It just doesn't make sense why they changed established naming conventions. Is this something that causes me sleepless nights? Not in the least. But it's still an annoyance for consumers and even advanced users as detailed in that latest Geerling video et al.
Possibly they stick with it because it's usable (ish) and it was driving everyone up the wall when they'd change it?
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.
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
... and the bunch of proprietary voltage schemes like Quickcharge.
Thanks to the EU those are now forbidden, all phones and laptops should be compatible with USB-PD.
Update: USB-PD is a requirement, but manufacturers are allowed to have their own proprietary charging solution.
I still don't understand why MacBooks support USB4/Thunderbolt 4/5, but NOT USB 3.2 Gen 2x2. So you can get 20-40Gb/s speeds with more expensive external disks, but only 10Gb/s with the cheaper, more commonly available ones that advertise 20Gb/s.
I believe it’s that MacBooks support Thunderbolt primarily and USB only where absolutely necessary beyond what’s coded into one of the TB specs; and I assume TB doesn’t define 3.2x2x2 as part of any TB spec <=5?
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.
Related. Others?
USB Cheat Sheet - https://news.ycombinator.com/item?id=31271038 - May 2022 (168 comments)
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
I have a USB hub that I bought recently, that has very nice markings on it that are almost like you say :)
I connects via USB4 to the host, and has the following markings on its ports:
- Power in/USB 10Gbps
- USB 10Gbps
- USB 10Gbps
- 8K HDMI
Pretty happy with this one so far.
> I think USB 4 is finally going to the right direction.
USB 4 is actually going into an even worse direction. USB 4 = Thunderbolt 4, except everything is optional. e.g. USB 4 might not even support DP Alt mode. Thunderbolt 4 always will.
Even backwards compatibility is optional in USB4. There are USB4 devices (SSDs at least) that will not function when connected to USB 3 ports.
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.
Or it could be: 5 Gbps --> USB 3 10 Gbps --> USB 3.1 20 Gbps --> USB 3.2
Higher number = better
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.
> and power of up to 240 watt
Except active optical cables. None exist yet that I'm aware of though.
I'd guess that most people who use optical Thunderbolt cables are aware that they do not carry power.
IMHO USB 3.0 was the last sanely-named version. Then again, if you're familiar with Ethernet, the proliferation of variants isn't unexpected.
Great way of identifying the difference in types of USB
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.
If you buy Thunderbolt 5 cables: every USB standard is compatible and then some.
It wasn't until last year that I finally purchased my first USB-C device/cables – and after years of solid DisplayPort and Thunderbolt2 connections I absolutely hate USB-C (it's too delicate, physically).
Not until 2023 did I even have a computer newer than 2012, so I missed almost all of USB3's hayday — including nomenclature disputes — but the speeds sure are an improvement!
I just wish product listings were clear and actually followed the specs.
This is generally good but it’s missing low speed (1.5 megabits/second), which is also under USB 1.1.
Where does TB5 come into all of this?
- 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)
I don't see why it would. Thunderbolt is not a USB standard
> 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...
Thunderbolt 5 and USB4v2 are the same thing now. They both support 80gbps and pcie pass through.
> 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.
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.
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.
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.
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.
nice work, thanks
[flagged]
You need to relax buddy, it's just a post on a web forum, why are you so angry?