USB data · 2019
USB4 (20 and 40 Gbps)
Thunderbolt 3's protocol, opened up as a USB standard. Tunnels USB, DisplayPort and PCIe over one cable.
- data: 20 or 40 Gbps
- video: DisplayPort tunnelled
- power: USB PD required
Spec card
- Link rate
- 2 lanes × 10 Gbit/s (20 Gbps) or 2 lanes × 20 Gbit/s (40 Gbps)
- What it carries
- tunnelled USB 3, DisplayPort and (optionally) PCIe
- Connector
- USB-C only
- Charging
- USB Power Delivery required on hosts
- Max passive length
- 0.8 m at 40 Gbps; about 1 m at 20 Gbps
- Thunderbolt 3 compatibility
- optional for hosts, so check
Also sold as USB4 Gen 2x2 (20Gbps)USB4 Gen 3x2 (40Gbps)USB4 20GbpsUSB4 40GbpsUSB 40Gbps
The cable you need
A cable marked USB4 40Gbps (or USB 40Gbps, or Thunderbolt 4). Thunderbolt 3 passive cables up to 0.5 m also run at 40 Gbps.
Watch out for
- A "USB4" laptop port may be only 20 Gbps.
- PCIe tunnelling and Thunderbolt 3 compatibility are optional, so some eGPUs and docks won't work.
USB4 is not just "faster USB". It is a tunnelling link: one fast pipe that carries USB 3 data, DisplayPort video and, if the host supports it, PCIe for things like external SSDs and graphics docks, all at once and shared on demand. It was built from Thunderbolt 3, which Intel contributed to the USB Promoter Group.
Two speeds exist. A host can be USB4 at 20 Gbps and still be USB4, so "USB4" alone on a laptop spec sheet does not mean 40 Gbps. Look for "USB4 40Gbps" or a Thunderbolt 4/5 logo, which guarantees 40 Gbps.
For displays, a USB4 port sends DisplayPort through the tunnel, so a monitor or dock needs no special mode. A 40 Gbps link has room for two 4K 60 Hz streams, or one high-refresh 4K stream, with USB data alongside.
What it can carry
Computed from each link's usable bandwidth; 4K at 60 Hz and above assumes 10-bit HDR colour. How.
| Mode | Thunderbolt 4 |
|---|---|
| 1080p 60 Hz 8-bit | Fits 3.2 Gbps |
| 1080p 144 Hz 8-bit | Fits 8.0 Gbps |
| 1440p 144 Hz 8-bit | Fits 14.1 Gbps |
| 4K 30 Hz 8-bit | Fits 6.2 Gbps |
| 4K 60 Hz 10-bit | Fits 15.7 Gbps |
| 4K 120 Hz 10-bit | With DSC 32.3 Gbps |
| 4K 144 Hz 10-bit | With DSC 39.2 Gbps |
| 4K 240 Hz 10-bit | With DSC 68.6 Gbps |
| 8K 60 Hz 10-bit | With DSC 62.1 Gbps |