The team states that its system memory can be maxed out at 1.5TB with six-channel memory across 12 DIMM slots. It also has eight PCI Express slots, two USB-C / Thunderbolt 3 and two USB-A ports.
With this Mac Pro, Apple is presenting a custom expansion module called an MPX Module with a dedicated Thunderbolt 3 backbone that Apple built into the motherboard for additional power and high-speed connectivity to components. It is basically a quad-wide PCIe card that can feature two graphics cards, its own dedicated heat sink, and a custom Thunderbolt connector.