About USB4


Tom dives back down the USB rabbit hole to explain recent changes and several updates to the most recent USB specification.

Featuring Tom Merritt.



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Episode transcript:

This episode ABOUT USB4 was originally released an episode about USB in March 2021, but several updates have happened since the the most recent in October. This episode includes updated information.

Enough of the preamble. Begin About USB4

I hear I can now get stuff with USB4. What the heck does that get me?
USB has been a mess and confusing and I don’t know if I want another number?
Also it relates to Thunderbolt 4 somehow?
Are you confused?
Don’t be.
Let’s help you Know a Little more about USB4.

USB stands for the Universal Serial Bus, a standard released first in 1996 to provide an industry standard for connecting peripherals and computers.
It is maintained by the USB Implementers Forum or USB-IF, a non-profit group founded in 1995 by Compaq, Digital, IBM, Intel, Microsoft, NEC and Nortel – it’s expanded its membership since of course.
Friends, before USB, each peripheral had its own connector and you couldn’t use the same wire or port for the other. Well there were a few exceptions but for the most part, a monitor had a VGA connector, a printer used a serial Port, a mouse used a PS/2 port and examples like that were many.
People at the founding companies of the USB-IF got together in 1994 to fix that mess and make it easier to plug things into computers and make it cheaper to make the computers because you didn’t need a separate port for every single peripheral someone might want to connect.
A team at Intel led by Ajay Bhatt produced the first integrated circuits to support USB in 1995. And Joseph C Decuir credited his work on the Atari SIO 8-bit communication implementation as the basis of the standard.
The USB 1.0 specification was officially released in 1996 and supported 1.5 megabit/second low speed and 12 megabit per second full speed data transfers. The high speeds were meant for printers and floppy drives, the lower speeds for cheaper peripherals with unshielded cables like joysticks and your mouse.
Microsoft began supporting USB in Windows 95 OSR 2.1 in August 1997. Apple’s iMac was the first mainstream product to support it and popularize it starting in August 1998.
It took off from there.
USB 2.0 arrived in April 2000 adding a higher signaling rate of 480 megabits per second and adding the Mini and Micro connectors.
USB 3 came along in November 2008 bringing superspeed capability at 5 gigabits per second and the blue ports to designate them. USB 3.1 followed in December 2014 doubling the speed to 10 gigabits per second called SuperSpeed Plus. And USB 3.2 arrived in September 2017 allowing for multi-lane operation to get data rates of 20 gigabits per second.
That brings us to the present. USB4 was released as a spec on August 29, 2019. And when you’re searching for info remember that unlike previous specs the USB-IF spells USB4 without a space between the B and the 4. All one term USB4.
While USB 3.2 was designed for use over USB-C cables – you know the small reversible ones–, USB4 is the first spec to require it. USB4 does not run over previous USB ports or connector types without an adapter.
ALSO USB 4 incorporates Intel’s Thunderbolt 3 spec. A USB4 host or peripheral device does not have to support Thunderbolt 3 but it can. The spec does require USB4 docks to support Thunderbolt 3 and hubs to support Thunderbolt 3 on the downward-facing ports – aka the one that peripherals plug into.
USB4 is mostly an attempt to simplify USB. The spec itself can be said to just tunnel other specs, like Thunderbolt, DisplayPort, USB 3.2, USB 2.0 and PCIe. It is therefore backwards compatible with all of those.
Also a USB4 connection requires USB Power delivery of at least 7.5 Watts per port up to 240 watts. So no more trying to guess if a USB port provides power or not by looking for the little lightning logo. It does. And it will make sure it only sends as much power as your device can handle.
The first products supporting USB4 arrived near the end of 2020 and the connector became common in new products released in 2021.
So what do you get if you get USB4?
USB 4 can share a single link with multiple end device types. So you can daisy chain. AND you get speed. USB4 devices must support 20 Gigabit per second data and can support up to 40 gbps data. And with video you can get an even faster effective rate. We’ll talk about that in a minute.
So while USB4 does simplify things quite a bit over previous USB versions you still have to check a device to know whether you’ll get 20 or 40 gbps. To help with that, packaging for certified devices can use simplified logos.
Starting from September 2022, you won’t see the words ‘SuperSpeed” or ‘USB4″ on packaging from certified USB providers. Since USB is an open standard, not every company will play along. However, if you’re looking at a certified products you will now see the highest data performance level that the product supports. So 40, 20, 20 or 5 Gigabits per second. If you’re looking at a USB cable you’ll also get the wattage of power that cable supports, so 60 or 240. Older designations for USB 2.0 and 1.0 are staying around. Which means if you see USB ‘High Speed” that means USB 2.0 which means a very not high speed 490 Megabits per second. And the rules don’t affect things like DisplayPort and Thunderbolt which USB can support, but is not officially part of the USB-IF’s own standards. So you’ll need to check separately for Thunderbolt compatibility.
Intel is no longer charging for implementation of Thunderbolt 3. And Thunderbolt 3 uses the USB-C connector just like USB4. That means a new computer with a USB4 port could offer compatibility with your existing Thunderbolt 3 devices. Could but not must. The spec makes it optional. Most devices seem to be implementing it because why not, but you will want to make sure it’s there if it’s important to you.
So how does Thunderbolt 4 fit in? Well some are looking at it is that Thunderbolt 4 gives you USB4 at its highest capacity with all its options. We have a whole separate episode on Thunderbolt 4 if you want all those details.
As I mentioned a minute ago, there’s also a situation where USB4 can handle more than 40gbps. That’s because it can also support DisplayPort Alt Mode 2.0 for high resolution displays. If that DisplayPort spec is implemented in a USB4 device it can transmit video data– just video data– at 80gbps meaning you can power multiple DisplayPort 2.0 displays at 8K and 60Hz refresh rate or one 16K monitor at 60 Hertz. And yes, a bunch of 4K monitors if you have that many. It achieves this by using all the lanes to send video data and leaving none to receive. So to get that speed you won’t share the connection with anything else but monitors.
Also if you’re not using every lane for display purposes, USB4 is smarter than USB 3.2 in how it allocates bandwidth. You could do that on previous USB versions but the lane would be split 50-50.
USB4 can divide up its capability dynamically. If you have a USB4 device that can support 40gbps, Your 4K monitor could be given 12 Gbps and your external hard drive would use the remaining 28 Mbps all on the same connection.
Oh and what about cables. Well good news your old cables will work. And other news. they won’t always work faster than they used to, except in a couple of cases I’ll mention in a second. If you have a 5gbps cable that’s all you’ll get out of it. However they brought in some exceptions
Now after USB4, the USBIF, indicated that there would be no more point versions of USB. And that the successor to USB4 would be USB5.
But that wasn’t the end for USB4. On September 1, 2022 the USBIF announced USB4 Version 2.0. Not USB 4.1. USB 4 Version 2. Technically not a point upgrade. It’s a version. It’s an update to the USB spec that enables 80 Gbps data performance over a USB-C cable and connector. Previously USB4 maxed out at 40 Gbps. The faster speed will be available over existing 40Gbps USB-C passive cables and newly-defined 80Gbps USB-C active cables. And for certain applications it can be configured asymmetrically to deliver up to 120 Gbps in one direction and 40 in the other direction. The most common use case is expected to be a computer sending 120 Gbps to a display. The new spec also enables USB 3.2 data tunneling to be faster than 20 Gbps and aligns with the latest versions of DisplayPort and PCIe. USB 4 Version 2 was published October 18th 2022 and added 80Gbps to the labeling scheme.
USB4 can now go faster over some existing cables if you have a USB4 Version 2.0 port. You can tell if your vendor calls it that but they don’t have to. They can also label the port USB 80Gbps, though in some specific cases it can do 120 Gbps in one direction. However you get it, if you get it, it will be good for your storage devices, your hubs, your docks, and your displays.
The next version of USB is intended to be called USB5. Simple. Hopefully. Barring USB4 version 3.
I hope this helps you cut through the confusion. Thankfully the USB-IF has helped us do that. Thanks USB-IF.
In other words I hope now you know a little more about USB4.