According to support documents published by Apple and spotted by MacRumours, the two Thunderbolt 3 ports on the right of the new 13-inch MacBook Pro 2016 are not as fast as the two on the left. The surprising bit of information was not covered during the device’s unveiling last week and is not publicised anywhere on the product listing or specifications pages on Apple’s website, which means that many users might not find out about this unless they specifically search for information when troubleshooting.
Apple has not quantified the differences in speed between the two sets of ports, but has stated that this applies only to the Touch Bar-equipped 13-inch MacBook Pro. The 13-inch model without Touch Bar and Touch ID has only two Thunderbolt 3 ports, and all four of the ports on the 15-inch model operate at full speed. This is due to limited availability of PCIe bandwidth across the device.
The news could affect users who attempt to daisy-chain multiple peripherals such as docking stations, storage devices, and the new 4K and 5K monitors developed jointly by Apple and LG.The multi-purpose Thunderbolt 3 standard, backed by Intel, is supposed to enable speeds of up to 40Gbps using the same physical ports, though the two on the right of the 13-inch MacBook Pro with Touch Bar will “vary slighty” according to Apple. However, USB 3.1 (Gen 2) transfers at 10Gbps are not be affected on any model.
The support document also outlines a number of other interesting facts. For instance, it was announced that users can plug a charger into any of the four Type-C ports now that MagSafe has been deprecated, but we now also know that the MacBook Pro will will sense the one that the highest capacity charger is plugged into and use only that. The 15-inch MacBook Pro 2016 comes with an 87W adapter and charge best at 85W, while the 13-inch models come with a 61W adapter and charge best at 60W. Apple warns that some docks and breakout adapters, including its own, pass only 60W through, so the larger model should ideally be used only with its own charger.
When plugging external devices into a MacBook Pro 2016 to charge or operate, the 15-inch and 13-inch models with four Type-C ports will provide up to 15W to the first two and then 7.5W to the second two in the order that they are plugged in, irrespective of port and device type. The 13-inch model with only two Type-C ports will provide 15W to the first device and 7.5W to the second.