Thunderbolt 3 Cable, Port and Power Performance Expectations
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Thunderbolt 3 Cable, Port and Power Performance Expectations

March 28, 17 - Posted in: Tech Talk by Kevin Quinn, Thee DocKtor
Thunderbolt 3 Cable, Port and Power Performance Expectations

Thunderbolt 3 bandwidth is shared bandwidth which means all connected devices will use the bandwidth for all protocols that transfer through the same Thunderbolt 3 cable (DisplayPort over USB-C traffic and traffic such as USB, Ethernet, and Audio).


It is important to understand the effects of Thunderbolt 3 cables used between Thunderbolt 3 ports for both power capability and data rates. Consider whether the connection is Host to Device (i.e. PC to Monitor), Host to Host (i.e. 20Gbps Thunderbolt Networking), or Device to Device (i.e. 40Gbps Daisy Chaining). Popular Thunderbolt 3 cables designs arranged in increasing relative price include:

  • 0.5m Passive 40Gbps, 5A (typically $30 SRP)

  • 1m Passive 20Gbps, 5A

  • 2m Passive 20Gbps 3A

  • 1m Active 40Gps, 5A

  • 2m Active 40Gps, 5A (typically $80 SRP)


Also, Thunderbolt 3 ports can be configured with 2 or 4 PCIe lane designs. Systems with the 2-lane designs will only support up to 20 Gbps data transfers. Systems with 4-lane designs will support up to 40 Gbps. An example of this is the new MacBook Pro 13-Inch Model. Per Apple, "MacBook Pro models introduced in 2016 very slightly in the data speeds they provide to each Thunderbolt 3 port."

  • MacBook Pro (15-inch, 2016) delivers full Thunderbolt 3 performance on all four ports.

  • MacBook Pro (13-inch, 2016, Four Thunderbolt 3 Ports) supports Thunderbolt 3 at full performance using the two left-hand ports. The two right-hand ports deliver Thunderbolt 3 functionality, but have reduced PCI Express bandwidth. Always plug higher-performance devices into the left-hand ports on MacBook Pro (13-inch, 2016, Four Thunderbolt 3 Ports) for maximum data throughput.

  • MacBook Pro (13-inch, 2016, Two Thunderbolt 3 Ports) delivers full Thunderbolt 3 performance on both ports.

Note, while the new 2016 MacBooks may have two separate full DP1.2 video stream implemented on their USB Type-C Thunderbolt 3 port, they do not support MST. Therefore, using a DisplayPort Alternate Mode dock (Targus DOCK410) will support only dual mirrored, not extended, display monitors. The chart below shows the number of lanes in popular Dell platforms. Please note that the Intel Alpine Ridge Thunderbolt controller uses separate inputs for Display Port 1.2 data (DP stream is not part of PCIe traffic).


The capability to source (provide) or sink (take) power varies by manufacturer and model. Many hosts with compatible protocols, will establish a USB Type-C Power Delivery (PD) contract with PD devices (docks, power supplies, monitors) at power levels less than the power supply that came with them. In an example, the MacBook Pro 15 inch will establish a PD contract for power and charging at 60W (20VDC @ 5A), well below the 87W that the PSU that came with it can supply. To determine the expected performance of various end devices connected through a docking station, it is often necessary to "do the math" to determine what speeds and feeds are supported. Feel free to contact Thee DocKtor at Targus for help.

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