Radeon Pro W6900X MPX Module

The Radeon Pro W6900X is a GPU that was developed by AMD as an optional MPX module for the 3rd-generation Mac Pro. Up to two can be installed at a time and it supports Infinity Fabric Link to increase the speed of inter-GPU data transmission by up to five-fold.

Description
The Radeon Pro W6900X MPX Module is based on AMD's high-end Navi 21 workstation graphics chip that was fabricated on the 7 nm process. The GPU base clock speed was 1.825 GHz, which could be boosted to 2.15 GHz, producing up to 22.2 teraflops. It contained 32 GB of GDDR6 video RAM, running at 2 GHz. It features one HDMI 2.0/2.1 port and four USB-C compatible Thunderbolt 3 ports. It could support three 5K or 6K displays, or six 4K displays. The first Thunderbolt 3 port and the HDMI port shared a PCIe lane, reducing the output of that Thunderbolt 3 port if the HDMI port was used. The MPX module took up the space of two double-wide PCIe cards, but did not require an auxiliary power cable as it could draw all necessary power from the proprietary MPX connector.

Release
On August 3, 2021, Apple began offering the Radeon Pro W6900X as a higher-performance alternative to the preceding Radeon Pro Vega II MPX Module, though the older version did remain on sale for existing users who wished to add a second matching module. The Infinity Fabric Link of the newer MPX modules are not backward compatible with the previous generation.

Practical tests indicated performance that was modestly better than its lower-cost sibling, the Radeon Pro W6800X MPX Module, and significantly better than the previous-generation Radeon Pro Vega II.

Issues
Apple is known to have shipped a Radeon Pro W6800X MPX Module mislabeled as a Radeon Pro W6900X, which brought up concerns about the effect on resale value. A reviewer stated that arranging an exchange for a similar issue had been challenging as Apple Support insisted that such situations were an anomalies.