USB4: Key Facts You Need to Know

USB4 is the latest USB standard that delivers up to 40 Gbps data transfer, supports DisplayPort and PCIe, and unifies Thunderbolt 3 compatibility. You need to know its speeds, cables, ports, and how it differs from older USB versions before buying devices.

What Is USB4?

USB4 is a specification released by the USB Implementers Forum (USB-IF) in 2019. It is based on the Thunderbolt 3 protocol, which Intel contributed to the USB standard. The main goal was to create a single, fast, and versatile connection that could handle data, video, and power over one cable. USB4 uses the USB-C connector exclusively, so you will not find it on older Type-A or Type-B ports.

Unlike previous USB generations that focused mainly on speed, USB4 integrates multiple protocols into one link. It can tunnel DisplayPort for video output, PCIe for external GPUs or NVMe drives, and USB 3.x data simultaneously. This makes it a true universal port for laptops, tablets, and even some phones.

Key Speeds and Generations

USB4 defines two speed tiers: 20 Gbps and 40 Gbps. The 40 Gbps version is the maximum and matches Thunderbolt 3. However, not all USB4 devices support the full 40 Gbps; some budget laptops only implement 20 Gbps to cut costs. You can check the specs of your device to see which tier it supports.

• USB4 20 Gbps – half the bandwidth, still faster than USB 3.2 Gen 2×2 (20 Gbps) but with the same tunneling features.
• USB4 40 Gbps – full bandwidth, equivalent to Thunderbolt 3, supports two 4K displays or one 5K/8K display.

It is important to note that USB4 does not change the maximum power delivery; that is handled by USB Power Delivery (USB PD) which can supply up to 240W with the latest spec. USB4 ports can negotiate power independently of data speed.

Thunderbolt 3 and 4 Compatibility

One of the biggest selling points of USB4 is that it is compatible with Thunderbolt 3. That means a USB4 port can accept a Thunderbolt 3 device (like an external GPU or a Thunderbolt dock) and run it at full speed, provided the host supports the required features. However, not all USB4 ports are certified for Thunderbolt 3; the USB-IF allows optional certification, so some manufacturers skip it to save costs.

Thunderbolt 4, released in 2020, is a stricter certification based on USB4. It guarantees 40 Gbps, supports two 4K displays, and requires PCIe 32 Gbps for storage. Thunderbolt 4 ports are always USB4 compliant, but USB4 ports are not necessarily Thunderbolt 4. If you need guaranteed performance, look for the Thunderbolt 4 logo.

Cables and Connectors

USB4 uses the USB-C connector, which is oval and reversible. However, not every USB-C cable is a USB4 cable. There are three main types of USB-C cables: USB 2.0 (for charging and basic data), USB 3.x (up to 20 Gbps), and USB4 (up to 40 Gbps). The cable must be certified for USB4 to achieve the highest speeds.

USB4 cables are typically marked with a 40 Gbps logo or the USB4 name. They are also thicker because they require more shielding for high-speed differential pairs. Length matters too: passive USB4 cables are usually limited to 0.8 meters for 40 Gbps, while active cables (with built-in chips) can reach 2 meters or more. If you need a longer cable, look for an active one.

How to Choose a USB4 Device

When buying a laptop, dock, or external drive, check the specifications for “USB4” and the speed tier. Also verify if the port supports DisplayPort Alt Mode and PCIe tunneling, as some implementations may omit them. For example, a USB4 port on a budget laptop might only support USB data, not video output.

Consider these factors:

• Speed tier: 20 Gbps vs 40 Gbps – decide based on your needs (e.g., external SSD speeds).
• Thunderbolt certification: If you plan to use Thunderbolt devices, ensure the USB4 port is certified.
• Power delivery: Check the wattage supported (e.g., 60W, 100W) to charge your laptop.
• Display support: Look for DP Alt Mode support if you want to connect monitors.

For cables, always buy certified USB4 cables from reputable brands to avoid performance issues.

Common Problems and Misconceptions

A frequent misconception is that USB4 is the same as USB-C. USB-C is just the connector shape; USB4 is the protocol. A USB-C port might only support USB 2.0 speeds, so always check the specs.

Another issue is that USB4 does not automatically mean Thunderbolt 3 support. Some manufacturers implement USB4 without the Thunderbolt certification, so you may not be able to use Thunderbolt-only devices. Also, using a USB4 cable with a USB 3.2 port will only give USB 3.2 speeds, not 40 Gbps.

If you experience slow speeds, it could be due to a poor-quality cable, incorrect port selection, or the device not supporting the full USB4 spec. Always use the cable that came with your device or a certified USB4 cable.

USB4 vs. USB 3.2 vs. Thunderbolt 4

USB4 is a major leap over USB 3.2. While USB 3.2 Gen 2×2 offers 20 Gbps, USB4 doubles that to 40 Gbps and adds protocol tunneling. Thunderbolt 4 is essentially a certified version of USB4 with guaranteed features. Here is a quick comparison:

• USB 3.2 Gen 1: 5 Gbps, USB-C or Type-A, no tunneling.
• USB 3.2 Gen 2: 10 Gbps, USB-C or Type-A, no tunneling.
• USB 3.2 Gen 2×2: 20 Gbps, USB-C only, no tunneling.
• USB4 20 Gbps: 20 Gbps, USB-C only, tunneling optional.
• USB4 40 Gbps: 40 Gbps, USB-C only, tunneling required.
• Thunderbolt 4: 40 Gbps, USB-C only, mandatory tunneling and certification.

Frequently Asked Questions

Is USB4 the same as Thunderbolt 4?

No. USB4 is a base specification, while Thunderbolt 4 is a certification that requires specific features like 40 Gbps, dual 4K display support, and PCIe 32 Gbps. All Thunderbolt 4 ports are USB4 compliant, but not all USB4 ports meet Thunderbolt 4 requirements.

Can I use a USB4 cable with a Thunderbolt 3 device?

Yes, if the USB4 port is certified for Thunderbolt 3 compatibility. Most USB4 ports support Thunderbolt 3, but check the device specifications to be sure. The cable itself must be rated for 40 Gbps.

Does USB4 work on any USB-C port?

No. USB4 requires a USB4 controller in both the host and the device. A USB-C port on an older laptop may only support USB 3.2 or even USB 2.0, so you will not get USB4 speeds.

Why is my USB4 device only getting 10 Gbps?

Possible reasons include using a non-certified cable, plugging into a USB 3.2 port, or the device itself only supporting USB 3.2. Also, some USB4 ports on budget devices may only support 20 Gbps, so check the spec.

Will USB4 replace Thunderbolt?

USB4 incorporates Thunderbolt 3 technology, but Thunderbolt 4 exists as a higher certification. It is likely that USB4 will become the standard for most devices, while Thunderbolt 4 remains for high-end professional use.

Can I charge my laptop with any USB4 port?

Not necessarily. Power delivery is separate from data speed. The port must support USB PD and the wattage required by your laptop. Check the power rating of the port and the charger.

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