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mib01

macrumors member
Original poster
Nov 8, 2022
49
10
Hello, is a USB 4 cable compatible with Thunderbolt 3 at 40gbps? Or just a native Thunderbolt 3 cable?

Initially a USB C 10gbps cable would work for me, but the price difference is small.

In the Macbook Pro 15 2017 system report it says Thunderbolt/USB4 ports 40gbps.



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Last edited:

PaulD-UK

macrumors 6502a
Oct 23, 2009
817
414
USB4 allows for a lower data rate of 20Gbps as well as 40Gbps, so a USB4 cable should be marked as to what speed it can transfer.
If its not marked assume it probably isn't high speed.
Longer cables over 1m in length are often not capable of 40Gbps.

Thunderbolt3/4 cables are required to have their manufacture/performance certified by Intel, and the plug ends and packaging be marked as to their data transfer rating.
TB3/4 cables over about 0.8m in length are required to have 'active' circuitry in the plug ends to maintain their full performance.

Longer USB4 cables may or not be active, but there is a speed rating marking system.

The USB4 standard includes the TB3 protocol within its specification (at 20/40Gbps, as marked), so is fine for TB3.
 
Last edited:
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mib01

macrumors member
Original poster
Nov 8, 2022
49
10
USB4 allows for a lower data rate of 20Gbps as well as 40Gbps, so a USB4 cable should be marked as to what speed it can transfer.
If its not marked assume it probably isn't high speed.
Longer cables over 1m in length are often not capable of 40Gbps.

Thunderbolt3/4 cables are required to have their manufacture/performance certified by Intel, and the plug ends and packaging be marked as to their data transfer rating.
TB3/4 cables over about 0.8m in length are required to have 'active' circuitry in the plug ends to maintain their full performance.

Longer USB4 cables may or not be active, but there is a speed rating marking system.

The USB4 standard includes the TB3 protocol within its specification (at 20/40Gbps, as marked), so is fine for TB3.
In the specifications it says 0.8 meters and TB3 support. In addition to being PD 100w that can be used on MagSafe 87w.
 
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