Thunderbolt 4 and 5 side by side
Thunderbolt uses the same oval connector as USB-C, but Intel certifies every product against higher minimums. Intel lists these figures:
- Thunderbolt 4: 40 Gbps, PCIe data at 32 Gbps (storage up to 3,000 MBps), two 4K displays or one 8K display, PC charging on at least one computer port (for thin and light laptops that need up to 100 W), and universal cables up to about 6.6 feet (2 meters).
- Thunderbolt 5: 80 Gbps both ways, with Bandwidth Boost up to 120 Gbps in one direction and 40 Gbps in the other when video traffic needs it, PCIe data at 64 Gbps, and charging up to 240 W on some devices.
At those link speeds, 1 TB takes 3m 20s at 40 Gbps, 1m 40s at 80 Gbps and 1m 6s at 120 Gbps, before overhead and the drive's own limit.
The PCIe path sets storage speed
The PCIe figure is what an external SSD or GPU enclosure can use. Thunderbolt 4's 32 Gbps is 4 GB/s, and Thunderbolt 5's 64 Gbps is 8 GB/s. The Throughput Visualizer models a Gen 4 drive reading at 7,000 MB/s, so a Thunderbolt 4 enclosure can't let it run at full speed. A Thunderbolt 5 link has room for that drive on paper, though the enclosure's own controller sets the final number.
What certification adds over USB4
Intel lists USB4 specification compliance for both Thunderbolt 4 and 5, so a Thunderbolt port is also a USB4 port. The certification adds minimums that USB4 leaves open. In Intel's comparison, USB4's minimum PC bandwidth is 20 Gbps, against 40 Gbps for Thunderbolt 4 and 80 Gbps for Thunderbolt 5, and accessory port power is 7.5 W against 15 W.
A certified port also brings Intel VT-d based DMA protection, which Intel requires to block physical attacks that read memory through the port, and mandatory certification for the product itself.
Cables, ports and the weakest link
A link runs at the speed of its weakest part: the computer's port, the cable and the device. For Thunderbolt 5 speeds all three need to be Thunderbolt 5, and a Thunderbolt 4 drive on a Thunderbolt 5 laptop runs at Thunderbolt 4 speed.
Because the connector matches USB-C, a bare USB-C port might be plain USB, USB4 or Thunderbolt. Look for the lightning bolt symbol and check the spec sheet.