USB4: Everything You Need to Know

A cable specification with the bandwidth for the future of gaming

USB is everywhere in the tech world. All modern devices have a USB port and most new ones come with a compatible cable for charging and data transfer. USB4 is no different in those terms, and in fact, it even uses the same USB-C cable that some existing USB devices require.

What is USB4?

Since USB4 is based on the Thunderbolt 3 standard, it’s twice as fast as the USB version before it, and it includes the video bandwidth of DisplayPort 2.0.

USB4 devices and cables won’t look any different from your typical USB 3 device, but behind the scenes are a few improvements that catapult it over previous versions, things you’ll especially care about if you’re an avid gamer.

You can expect devices to hit the shelves in 2021.

USB4 40 Gbps logo

USB Timeline

If you need a refresher, here’s a quick glance at the release date and bandwidth limits of the last few USB versions:

  • USB4: 2019; 40 Gbps
  • USB 3.2: 2017; 20 Gbps
  • USB 3.1: 2013; 10 Gbps
  • USB 3.0: 2008; 5 Gbps

That USB 3.x naming scheme is outdated but remains here for brevity. They go by new names now.

USB4 is More Than Speed

USB4 actually has two speed ratings: 20 Gbps for USB4 Gen 2x2 and 40 Gbps for Gen 3x2. The former is a requirement for all compatible hosts, devices, and hubs, while the latter is only mandatory for USB4 hubs.

That’s fast, there’s no question about it. But USB4 offers more than just additional speed:

Flexible Bandwidth

If you’re using more than one device at once, USB4 can understand how much bandwidth the devices need and supply each with a proper amount. For example, if you’re using a monitor and transferring data over an external hard drive, they’ll both work well enough on their own without sucking too much bandwidth away from the other device.

A similar feature, possible through DisplayPort 2.0 support, is USB4’s ability to switch to single direction mode. Tapping into the cable’s four lanes at once via DisplayPort Alt Mode allows it to use the full 80 Gbps for some really impressive bandwidth feats, like for a smooth display on an 8K monitor.

Powerful Charging

All USB4 devices will support USB Power Delivery (USB PD), which just means that they can be used for charging other devices. Your laptop, for example, can be used to charge your phone over USB4 just like it can with older standards. Or your monitor that’s plugged into the wall can be used to power your laptop.

However, much like how this new version of USB is faster when it comes to data transfers, it’s also able to deliver more power to your devices. Up to 100 watts can be supplied through a USB4 port, so if your device supports fast charging, you can expect even quicker power-ups. 

And similar to how data transfers are flexible depending on the devices being used, so too is power. Something like a laptop that requires more power, can use what it needs while lower-power devices like a flash drive or pair of headphones, can use less.

USB4 and Thunderbolt

It might be hard to understand how these two technologies are different. It’s difficult to keep track of it all when you see that USB4 is based on Thunderbolt 3 and that they’re somewhat interchangeable, but then you’re also told that they’re not technically the same since there's also Thunderbolt 4.

Years ago, Thunderbolt used the Mini DisplayPort connection, but when v3 came out, Intel switched over to USB-C. Also with this release, Intel allowed Thunderbolt to be used for free without paying royalties, so it’s less of a concern for hardware manufacturers to support it.

Following Thunderbolt 3, USB-IF announced USB4 and said that it would be based on the Thunderbolt 3 spec, meaning that it would adopt some of its features. What this leads us to is today, where we have all of what we talked about above: faster speeds, backwards compatibility, and more power output.

The idea is to allow more devices to work together in a unified system. Hopefully one day, you’ll be able to buy devices that work better with each other, without the need for so many adapters and device-specific cables.

Thunderbolt 4, however, which is the newest version, is a bit different. Its minimum PCIe support for storage is 32 Gbps instead of 16 Gbps in v3, and it allows cables 2 meters in length to operate at full 40 Gbps capacity. You can see some other differences between versions 3 and 4, and USB4, on Intel’s website.

What it all boils down to is increased compatibility for these device types and improved USB performance.

What About USB4 Compatibility?

According to the USB4 Specification, it’s compatible with USB 3.2 and Thunderbolt 3 hosts and devices. Those devices already use USB-C, so cabling isn’t an issue there. However, Thunderbolt 3 support isn’t required, so not all USB4 ports will necessarily accept all Thunderbolt devices.

USB4 is also compatible with USB 2.0, but since USB Type-A is physically different from USB Type-C, an adapter is required to make the physical connection. And just like any backwards compatible device, the speed is limited to the slowest of the two, which in this case would be 480 Mbps set by USB 2.0.

USB-C only describes the physical connection, so not all USB-C cables and ports support the 40 Gbps speeds. You’ll need a cable that specifies that it does, and you’ll need to look carefully at the devices you buy to ensure that they support the rates you’re wanting. A 40 Gbps-certified cable will be necessary to achieve those max speeds (or at least somewhere close to them), whereas your standard USB-C cable will be fine for USB 3.2 speeds (20 Gbps).

Again, since USB-C and Thunderbolt 3 ports look identical, it won't be immediately clear if the port you’re using will work with your Thunderbolt device since it might actually be a USB 3.2 port.

USB-IF recommends (but doesn’t require) that products are labeled with a clear indication of the data rates they support, such as USB4 20 Gbps or USB4 40 Gbps. They also suggest that products that comply with these performance levels use a special logo, but those guidelines aren’t yet completed.

The takeaway here is that data transfers and power usage vary between Thunderbolt and USB products, so knowing exactly what your device’s ports are and what type of cable you have will go a long way in knowing whether your devices can connect with each other and perform the way you want them to.