The detailed support document published by Apple for its new MacBook Pro lineup reveals that the full bandwidth offered by PCI Express over Thunderbolt 3.0 ports on its new 13-inch MacBook Pro with Touch Bar is limited to the two ports located on its left.
While all the four ports on the 13-inch MacBook Pro with Touch Bar features Thunderbolt 3.0 connectivity, the two on the right offer reduced PCI Express bandwidth. This means that on these two ports, the performance of devices that require high bandwidth can be limited. So, it is recommended that high-performance devices be connected to the Thunderbolt 3.0/ USB-C ports located on the left.
The other two MacBook Pro models that Apple unveiled last week — the 15-inch MacBook Pro with Touch Bar and the 13-inch MacBook Pro without Touch Bar — offer full PCI Express bandwidth on all their Thunderbolt 3 ports.
Late-2016 MacBook Pro models vary slightly in the data speeds they provide to each Thunderbolt 3 port.
MacBook Pro (15-inch, Late 2016) delivers full Thunderbolt 3 performance on all four ports.
MacBook Pro (13-inch, Late 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.
MacBook Pro (13-inch, Late 2016, Two Thunderbolt 3 Ports) delivers full Thunderbolt 3 performance on both ports.
The Thunderbolt 3.0 ports also allow daisy-chaining so you can have multiple devices connected to your new MacBook Pro from just one port. For example, you can connect one of LG’s new 4K or 5K monitor with the new MacBook Pro which in turn will also charge the laptop. The USB ports on the monitor can then be used to connect external storage devices or peripherals.
Additionally, all the USB-C ports on the new MacBook Pro lineup offer USB 3.1 Gen. 2 connectivity meaning that they are capable of providing transfer speeds of up to 10Gb/s. Any of the available USB-C ports can also be used to charge the MacBook, and if you attach multiple chargers to the laptop at once, it will only pull power from the highest rated charger.[Via MacRumors]