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USB4 Specification v2.0 (usb.org)
44 points by cesarb on Oct 19, 2022 | hide | past | favorite | 58 comments



Announcement: https://usb.org/sites/default/files/2022-10/USB-IF%20USB%208...

Specifications released today:

- USB4 Specification v2.0 <https://www.usb.org/document-library/usb4r-specification-v20>

- USB Type-C® Cable and Connector Specification Release 2.2 <https://www.usb.org/document-library/usb-type-cr-cable-and-c...>

- USB Power Delivery Revision 2.0 Version 1.3 and Revision 3.1 Version 1.6 <https://www.usb.org/document-library/usb-power-delivery>

Yes, they really called it "USB4 v2.0"...


Hardware revision numbering schemes can sometimes get wonky... but it's almost as-if the USB folks live in a bubble and are completely unaware of the meme their naming scheme has become.

There has got to be a more simple naming scheme that's easier to follow...


> it's almost as-if the USB folks live in a bubble and are completely unaware of the meme their naming scheme has become.

It's almost as if it was designed by a committee.


Run by the same companies that marked USB products


Semantic versioning would be just fine here I’d say; e.g. they could have named this USB 4.1 to indicate compatibility.

Alas, I suspect there are many conflicting desires here, and marketing may have something to do with it — the ability to convince customers into buying new hardware by confusing them may have something to do with it.


Hi, USB committee member here. I hear your concern and I’m officially launching the USB4 v2.0 naming schema v0.5b task force to analyze the naming schema. Thank you for your concern.


that name is the spec name, the marketing names have been cleaned up and are much more sane: https://arstechnica.com/gadgets/2022/09/usb-if-says-goodbye-...


> When those products come out, though, the USB-IF hopes they aren't introduced to consumers as "USB4 Version 2.0" or even some type of "SuperSpeed USB." After 12 years, the USB-IF no longer recommends that vendors use terms like "SuperSpeed USB 20Gbps" (for the spec called USB 3.2 Gen 2x2, for example) and instead opt for names like "USB 20Gbps."

> If the USB-IF had its way, products using its new open standard will be described as "USB 80Gbps."

Despite the ongoing chaos of USB-IF's technical nomenclature, it sounds like they are well aware of the problem, and the consumer-facing solution they recommend doesn’t sound bad at all.


Are they going to allow color-coding and icons to indicate what a cable or connector is capable of?


The new branding just has Gbps and Watts. The problem is that 99% of USB cables seem to be unlabeled knockoffs; no branding system can solve that problem.


I don't think that's a great excuse. It's find for companies to have internal and external (marketing) names for the same thing, but these are both public! They have two public names for the same thing which is arguably even more confusing.

Look at that article:

> The USB-IF still recommends vendors label USB 2.0, which can take the form of USB-C, USB-A, USB-B, and more, as "Hi-Speed USB" with no performance indicator. > > "Hi-Speed USB has been around for over 20 years and is well established in the marketplace"

They are seriously under the delusion that anyone except USB nerds has even heard of "hi-speed USB".


You're asking for the impossible.

To developers, the difference between USB 3.1 2x2 and USB 4 is material, and they need two different names.

To end users, they're identical, and different names are confusing.

Changing the labelling of USB 2.0 would be a cure worse than the disease. Approximately nobody is introducing new USB2 products, so having <1% of USB2 products use new nomenclature would only increase confusion rather than decrease it.


> To end users, they're identical, and different names are confusing.

They're not though are they? For example USB4 supports Thunderbolt 3 and PCIe tunnelling but USB 3.2 2x2 does not.


Those are optional features in USB4 so you might as well treat them as not existing.


More sane indeed; glad they realized it was completely non-sense. Thanks for sharing; the post you linked is actually much better than OP's link USB4 specs.


> Revision 2.0 Version 1.3 and Revision 3.1 Version 1.6

WTF?


I’m surprised they didn’t call it USB4 SuperSpeed


That probably will still make it as a product name, somewhere.


What does the "4" in USB4 mean? When does it change? Why did it change fairly frequently until recently (with minor versions like 3.1), but then stop at 4?

I had always assumed the number in the name was the spec version. But now the spec version is explicitly v2.0, but the "4" remains in the name. Why isn't this USB5.0?

It's not like USB ports are labelled with what USB version they support or anything, such that there would be valid reasons to have a "compatibility version" that stays at 4. USB ports are just labelled/colored according to a marketing term that loosely maps to supported link speed (Hi-Speed / black, Super-Speed / blue, etc.)

Is this a thing like X11 (the "11" was a protocol version number once upon a time!), where the major version in the name somehow gradually ossified and became hard to change, even as major things kept happening to the spec; and so they just gave up and made the version an opaque part of the name, and lifted the version out somewhere else?


Like anything, they have major versions and minor versions. USB4 was a new major version because it added Thunderbolt. USB4 2.0 (should have been USB4.1 but whatever) adds some minor changes.


USB4 moved from a lane-switched architecture to a packet switched architecture.

In USB3, for example, if you plug in a DisplayPort display via USB-C, there was an alt-mode negotiation, either 2 or 4 of the 4 lanes would switch over to become DisplayPort lanes (leaving you with either 2 or 0 lanes of USB3). Even if you have a 1080p60 (~4.3Gbps) monitor plugged in, you're still losing 20 of the 40Gbps because you're losing half the lanes.

In USB4, everything (except USB1 & USB2, lol) is tunneled over USB4. If you plug a hub in to a computer, and a display (or two or three) into a hub, the displays only take as much bandwidth as they need from the total link budget. Each 1080p60 monitor is taking 4.3 of the 40Gbps (or less, if the monitor has Display Stream Compression). Same goes for devices plugged in via PCIe/Thunderbolt.

There were a lot of weird architecture limitations because of the lane-switched architecture of USB3. It's more or less reason we almost never saw USB hubs with multiple USB-C ports: people would plug in a USB-C monitor, and maybe the hub could be smart enough for that, but plug in a second USB-C monitor, and now the DisplayPort lanes somehow need to serve two monitors. (This is actually achievable with DisplayPort's Multi-Stream-Transport hubs, but lack of support from Apple caused constant angst here.) With USB4 though, a hub can now just route packets, so you can imagine having multiple USB-C hubs fanning out & serving multiple displays; USB-C makes more sense now & has much less caveats under USB4.


Do you know what the max PCIe bandwidth in practice is? I suppose I'm asking about both right now, the next two years, and the further future of USB4 v2.

In the past there have been some significant limits, like Intel's thunderbolt chips only getting 22Gbps of PCIe data on a 40Gbps link.


Good question. I haven't heard any future plans.

My understanding is that TB3 reserved some of the throughput (for video, even if unused?), and then the remaining throughput went through 8b/10b encoding, which left ~26Gbps as the maximum theoretical PCIe bandwidth (significantly less (-18%) than the PCIe 3.0 x4 connection's 32Gbps).

I don't know if there's still restrictions that prevent PCIe from making more use of the link in USB4/TB4. That seemed like a weird restriction, and it'd be especially weird not to see such a big gap when there is USB4 80Gbps. Anyhow, the encoding at least has gone from 8b/10b (+25% overhead) to 64b/66b or 128b/132b (+3%), which I believe should boost TB4 numbers a little.

In practice, rather than the 26Gbps of PCIe it seems like we might be able to get, I've found similar-ish reports that a bit over 22Gbps was all TB3 could typically manage when doing a drive test... I don't know but I'd be very curious to get more details on where the missing 4Gbps are. How much do we lose to NVMe overhead, how much is lost to tunneling overhead, what other factors are there? I haven't heard any real data about what if any additional latency there is. One test I'd like to see is what happens to drive-speed as we go from direct attached, to 1 hub, to 2 to 3 hubs.

As for the future, lots of good questions there; I haven't stumbled into any juicy tidbits at this time. A simple boost to PCIe 4.0 is all too likely, but how great it'd be to specify something more general/generic. It'd be great to see tunnels that have either more fan-in or more fan-out than the underlying connection: here's 8 different PCIe 6 x1 devices plugged in, and yes they're oversubscribed but they all work fine, that'd be a lovely example to see. But that's probably pretty pie in the sky right now.


The announcement said they're aligning with PCIe 4.0. If we assume that's 4 lanes then hopefully it should support 40-50 Gbps of tunneled PCIe traffic.


> but whatever

I think people are asking - what really is the 'whatever' behind this version scheme?


They 4 is meaningless and confusing. Which is why all version numbers are being dropped completely on labels and marketing. https://arstechnica.com/gadgets/2022/09/usb-if-says-goodbye-...


So, if the USB IF agree on that point, why isn't this spec just called "USB Specification v5.0"? Like when the Linux kernel dropped the 2.x/3.x and just started incrementing major versions with every major release?


It would more be USB 4.1 not 5.0 as it's mostly the same as USB 4.0.

I think the reason why they went with 4 v2 is because they redefined some terminology. E.g. "USB 3.2 Gen2x2" / "USB SuperSpeed 20Gbps" is now "USB 20Gbps". But not sure.


I didn't mean that it was 5 as in the successor to 4. The standard itself wouldn't be named/referred to as USB5; it'd be named/referred to as just "USB".

Rather, the spec version — the part that's currently v2.0 — would become globally versioned over all future USB (no longer numbered) standard versions, rather than locally versioned per USB standard version.

By itself, that change would make the new standard "USB, specification v2.0".

But, obviously, that's confusing, since "USB2.0" was also a thing. In fact, starting the global specification-version numbering scheme with any major version number below 5, would make the spec version be confused with a USB standard version. So they'd pretty much have to "skip" to spec version 5.0 as the place to start counting from.

So the result would be "USB, specification v5.0".


The version number of USB always had been the specification, hence why you have e.g. "Gen2x2".

But this doesn't mean you want to bump the major version number without making any major changes to it, for example create a new (backward compatible) protocol instead of a new extension to the current protocol.

I mean if we look at it from various perspectives:

- for users it's still the exact same kind of USB, just better labels in the future so even just bumping it to 4.1 would be misleading and 5.0 could be said to be outright user hostile if you consider how it will be misused to sell things

- for tech people 4.1 probably would be the most appropriate but 5.0 would be still misleading

- for people working on usb tech it's also mostly the same and 5.0 would probably still cause additional friction about what needs and doesn't need to be done when discussing it with management

So IMHO 5.0 would be an horrible choice 4.1 would have been nice but I can understand why they didn't do it I think calling it revision 2 instead of version 2 would probably be the most appropriate, except if they already use revision for spelling/formulation improvements idk.

EDIT: In context of them adding a new major alternate mode 4.1 would have been the most appropriate. But then there was a lot of consumer confusion around 3.1, 3.2 and my point about it not being useful for consumers still holds as e.g. a USB 3.2 device doesn't need to support anything added since 3.1 so given that they want to make it less hostile for users it even somewhat makes sense no matter how stupid version 4.0 version 2 sound.


The new name is "usb 80gbps". That's better than usb5.


It all makes sense once you understand that they are trying to confuse us as much as possible.


Looking forward to USB4.1-C 2.0 4x4 Revision 1.1


What exactly is USB4 2.0? Why isn't it called USB 4.1?


I like the USB-C connector but wondering if there is a better way to handle the ever expanding number of different cable types that are used with this connector (SuperSpeed, Thunderbolt, etc).

Switching to USB-C reduced the number of different cables I have at home but almost equally increased the number of different types of USB-C I have. Some work with my monitor, some don’t, some charge, some don’t charge, it’s a mess.


If you want to, you can buy all 40 Gbps 240 W Thunderbolt 4 Pro USB-C cables for all use-cases, but they're literally like $100 a metre, so that'd be insane and why instead there's a variety of cheaper cables for different use-cases.


Exactly - it's too expensive and at this point I am not sure how future proof this investment would be. Are we going to have a new USB-C cable in a year's time that my next monitor will require?..

Edit: different devices add even more to this confusion. My MacBook Pro M1 is refusing to work with a 4K USB-C monitor even when using a Thunderbolt 4 cable. LG is convinced that it should be working just fine.


A USB-C 3.0 100W cable is more like $20 and does everything other than Thunderbolt. The OP must have really bad luck.


Where the heck did you get a cable that can't charge? Unless you mean it can't go over 60 watts?


Sorry, I meant data transfer+charging at the same time.


Every cable is suitable for at least USB 2.0 data transfer and 60W PD charging. Fully-featured cables get USB 3.0 data (at varying speed) and e-marked cables get >= 60W charging (100W or even higher with more recent PD revs). Thunderbolt (and USB4) has its own requirements.

If the above isn't true for your particular cable, it's either broken or what you're trying to do isn't specified by USB-C but rather some proprietary tech instead, in which case, blame your device vendor.


Interesting. I was testing this with a 4K USB-C monitor connected to MacBook Pro M1. Charging was not working due to "insufficient power".

I am trying to keep up with these spec details for a cable that is often marketed as just USB-C... it feels like an unnecessary cognitive load.


Unless you need to go above 60W, a cable does not have any way to influence negotiated charging profile at all.


We once had a world where we didn't have to think very hard, and could use most cables with most devices.

How do we get back to that world?


Ok so what event happened after USB 3.1 came out that made the USB committee lose their damn minds? Everything made perfect sense until then.


Im certain it does not support USB 3 Gen 2x2 (20 Mbps) devices :(


Why? When have they ever dropped compatibility, and what would their motivation be?


Beats me, but that was outcome when I searched last time. It will support at 10 Mbps, not 20


Well find those results if you can, because I can't find any rules restricting what speeds can bond together in the spec. USB4 mode has a minimum speed of gen2, but that shouldn't cause any problems here.

Is this supposed to be new with version 2? Wikipedia lists 2x1 and 2x2 among other speeds for USB4.


Are we finally going to get a round connector?


Does this mean I'll have to deal with another planned-obsolescence connector? I was hoping with Moore's law flattening out that we would more or less be done with this mess. USB-C does a great job, what's wrong with it?


USB-C is a connector.

USB4 v2.0 is a protocol.

Different things. No need to be this excited.


this is more than most non-techie people can handle.


Well that's too bad because most ports have multiple protocol versions or capacities over the same shape.


afaict it will still use the usb-c connector, they're just playing catch-up to thunderbolt as far as bandwidth. now you can do PCIe over USB4 just like thunderbolt. Although I haven't read the whole spec yet, likely it finally supports dual high-def monitors which USB4v1 didn't do


Pretty sure this is still using the USB-C connector.


Gonna disagree with all of the other comments so far: yes, you’ll have to deal with another set of USB-C connectors with a slightly different capability matrix.


Nah you'll have to wait for USB5 for the new connector




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