What is USB4?


USB4 is the latest generation of the Universal Serial Bus specification, opening up the potential for higher bandwidth data transfers, support for higher-resolution displays, better interchangeability with other connectors, and a simplified naming scheme, to boot. First announced in August 2019, the standard has taken a little while to get going, but many USB4 devices are now readily available, making it an exciting new connection option for anyone looking to connect external devices to laptops and desktop PCs.

The USB4 standard is based on the Thunderbolt 3 protocol, and shares many of its best features, including an up to 40 Gbps data transfer rate, the reversible USB-C connector type, the ability to handle video and data at the same time, and the potential for higher wattage power delivery.

USB4 is everything that was great about USB 3.2 Gen 2x2 and ratchets it up a notch, making it one of the most versatile connection options available today. Interested? Here’s everything you need to know about USB4.

From USB 1 to USB4

The USB standard is ubiquitous throughout the tech world. After all, “USB” is an acronym for “Universal Serial Bus,” and it’s had more than two decades to do its name proud. The standard has seen its fair share of updates over the 23 years since its introduction, each of which brought higher speeds, new features, and new connection types, and the latest generation is the most exciting and capable of the lot.

The USB standard was introduced in 1996 as a way to standardize peripheral connections under one specification. USB 1.0, the first USB specification, used the traditional, non-reversible Type-A connection on the host and offered transfer speeds up to 12 Mbps. USB 2.0 was introduced in 2001 and was much faster, operating at up to 480 Mbps. USB 2.0 also incorporated new form factors, including the Micro B port (commonly seen on older phones and external hard drives). USB 3.0 brought another speed bump in 2011, offering up to 5 Gbps transfer speeds. USB 3.0 saw a few iterations, primarily USB 3.1 in 2014 (up to 10 Gbps) and USB 3.2 in 2017 (up to 20 Gbps). 3.0 speeds were supported on multiple connector types including the standard A connector, B, and, micro-B, now ubiquitous Type-C connection. 

New features were introduced over the generations too, including the ability to transmit video, as well as data, and the option of super-fast charging using USB Power Delivery.

The next update to the USB standard is now here. After officially being announced by the USB Promoter Group on March 4, 2019, USB4 cables and devices are now available and ready for use. But what is USB4? In this article, we will discuss what the new specification brings and highlight its advantages over its predecessor USB 3.2 standard, in all its derivatives.

What are the main advantages of USB4?

The USB4 specification (officially known as “USB4,” written without space) has three key traits, according to the USB Implementers Forum (USB-IF). These include:

  1. Two-lane operation with up to 80 Gbps operation (over certified cables), using the USB Type-C connection, though more modest speeds like 40 Gbps, and 20 Gbps, will be more common;
  2. More efficient sharing between data and display protocols;
  3. Backward compatibility with USB 3.2, USB 3.1, USB 3.0, USB 2.0, and even Thunderbolt 3.
  4. Faster charging USB Power Delivery at up to 240W
  5. Support for up to DisplayPory 2.1 using DisplayPort Alt Mode over USB.

There is also the additional advantage of simplifying the naming scheme for USB. The previous generations of USB 3 grew incredibly confusing over their lifetimes. What began as USB 3, turned into USB 3.1 and USB 3.2, which in turn led to the recategorization of previous versions. They were all ultimately renamed as generations (or Gens) of USB 3.2, so USB 3.0 became USB 3.2 Gen 1, and USB 3.1, became USB 3.2 Gen 2. The maximum performance USB 3.2 version was ultimately called USB 3.2 Gen 2x2. 

USB4 starts afresh with a new generation of connectors, and though their speed can vary, there is at least a single generation that they are all a part of. All USB4 cables are USB-C, too, so the connector type does not need to be specified.

1. Significantly faster transfer speeds than USB 3.2

The first point is fairly straightforward and might seem like the most obvious advantage of USB4. Until the release of USB4, the fastest USB specification, USB 3.2 Gen 2x2, only offered transfer speeds up to 20 Gbps, though its 10 Gbps counterpart is far more common on devices. USB 3.2 Gen 2 transfers data at up to 10 Gbps, USB 3.2 Gen 1 (and all previous USB 3.0 and 3.1 specifications) operate at up to 5 Gbps. 

The original USB4 specification penned its maximum performance at 40 Gbps – the same as the Thunderbolt 3 protocol it is based off of. However, since then the USB Implementer’s Forum has also introduced a new USB 80 Gbps certification, which would grant some active USB4 cables the ability to transmit data at up to 80 Gbps – double that of even Thunderbolt 4. Compatible cables will be labelled with the unique 80 Gbps logo, and those able to deliver higher wattage power delivery to also have unique logos stating their potential wattage.

Like Thunderbolt 3, USB4 uses the USB Type-C connection. USB Type-C is the rounded, reversible connection seen on most modern Android phones and laptops. In addition to data, the USB Type-C construction also allows for display connections, which plays nicely into USB4’s second characteristic: dynamic bandwidth allocation for data and display connections. 

what is usb4?

2. Improved bandwidth allocation over USB Type-C

While other USB specifications can similarly transfer data and display information, they tend to have trouble with bandwidth allocation, splitting bandwidth evenly between connected devices. For example, if an external storage device and a display are connected to a computer through a USB Type-C dock, bandwidth will be evenly split between the display and the storage device. This can throttle the transfer rate of the storage device.

USB4 doesn’t have those issues because it can dynamically monitor bandwidth requirements for connected displays and save the rest of the bandwidth for data transfer. Previously, data could only be transmitted through the data lane and video could only be sent through the video lane. That means even if a connected display didn’t use an entire lane’s worth of bandwidth (5 or 10Gbps), the unused bandwidth couldn’t be allocated for data transfer and vice versa. Now data and video can share lanes and therefore share the total maximum bandwidth. This makes connecting multiple devices through a dock much more efficient.

3. Backward compatible with USB 2.0 and up

The introduction of the Type-C connector has already caused many consumers enough consternation, and the USB-IF is likely aware of this. So, not to immediately render other USB specifications obsolete, USB4 is backward compatible with everything from USB 2.0 to the latest USB 3.2 Gen 2x2 specifications. That is welcome news to users with legacy USB peripherals, though there is a small catch. While older USB devices will be able to connect to a USB4 port (using an adapter, if needed), the device will only be able to operate at the slower USB standard. For example, a USB 2.0 external hard drive will be able to connect to a USB4 port using an adapter, but transfer speeds will only occur at USB 2.0 speeds (up to 480 Mbps).

USB4 vs. Thunderbolt 3 vs. Thunderbolt 4

The USB-IF made it clear early on that USB4 would be backward compatible with Thunderbolt 3, but there are a few points to note. It is important to understand that the USB4 spec is based on the Thunderbolt 3 protocol, which Intel donated to USB. However, despite it being based on the TB3 protocol, support for TB3 is not mandatory for USB4. USB4 devices will need to be separately certified by Intel as “Thunderbolt 4 certified” to use the Thunderbolt logo. Thunderbolt 3 compatible USB4 ports will then be Thunderbolt 4 ports. This means that not all computers with USB4 will work with Thunderbolt 3 and Thunderbolt 4 peripherals at Thunderbolt 3 or 4 specifications, but will be able to operate at the full potential of that cable within the USB4 specifications.

As such, it is unlikely that Thunderbolt 3 will disappear from the PC landscape. While it’s likely we will see more USB4 desktops and laptops with AMD CPUs, they won’t always have Thunderbolt 3 support since they’d have to get separate Intel certifications. On the other hand, Intel-powered machines with USB4 are more likely to be compatible with Thunderbolt 3 since they’re already using Intel technology.  Put simply, USB4 can support Thunderbolt 3, but it doesn’t have to. Consumers should specifically note whether or not a new device supports Thunderbolt 3 via USB4 should they want to connect it to via Thunderbolt 3.

However, for those looking to maximize data transfer rates, the support for Thunderbolt on AMD-based PCs may not matter. USB4’s ability to transfer data at up to 80 Gbps and up to 240W of power, is unparalleled on even the best Thunderbolt 4 connection.

What else can USB4 do?

In addition to higher transfer speeds, improved bandwidth allocation, and backward compatibility, USB4 also offers a much more robust Power Delivery system. The original specification rated it for up to 100 Watts over its USB-C port. However, since then the USB Implementer’s Forum has released its USB4 2.0 specification that not only offers greater bandwidths of up to 80 Gbps on compatible active USB4 cables but also allows for an increase in USB Power Delivery to 240W, which makes for faster charging of even the most high-end of laptops.

Many USB-C ports prior to USB4 already supported some form of Power Delivery, but USB4 raises the potential charging power of the port considerably. Not all USB4 ports support the highest charging abilities, though, and the USB Implementer’s Forum has mandated that cables compatible with specific wattages sport logos to make it clear what they can deliver.

When implemented by the host, USB4 can also use intelligent Power Delivery. This allows a USB4 cable to deliver as much power as a connected device requests, up to 240W Watts. Even better, the Power Delivery over USB4 is bi-directional, allowing power to flow to and from a connected device. That can be particularly useful when it comes to connecting to external displays, as they can then use their main power source to charge a connected laptop.

USB4 uses DisplayPort Alt mode to transmit video to an external display, and can even be used to daisy chain multiple external displays together. Introduced with the USB-C connector in earlier generations of USB technology, USB4 leverages DisplayPort Alt mode in much the same way, although to an advanced standard. The original USB4 specification supported DisplayPort 1.4, but the newer USB4 80Gbps standard unlocks the option of DisplayPort 2.1 support, giving it the ability to transmit 4K video at up to 240Hz, or even handle a single 10K display at up to 60Hz.

Where to buy USB4 cables?

With USB4 cables now entering the market, it’s important to buy quality cables from a trusted company. Cable Matters offers a range of USB4 cables, including those that can handle 40 Gbps data transfers and up to 100W of USB Power Delivery. In the months to come as the USB4 specification is further expanded, look out for Cable Matters cables that support the new, higher-end 80 Gbps specification, and up to 240W of charging power.

Comments (2) -

  • Incredably clear, this article. Thank you..

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