They show up and for the right professional apps, you can use them combined - but differently than crossfire. Doesn't boost gaming much if at all, especially for the cost. .As for TR - can AMD make enough chips for them? And would they have needed a more complex design for cooling a chiplet based system than a monolithic die? I suspect that was the reason - and the existing agreement which might have had penalties for cancelling, etc. Known solution vs something new...?I'm genuinely surprised that Apple has stuck with Intel and not switched over to AMD Threadripper, Threadripper Pro or even Epyc chips. The improvement on the Mac Pro 2019's IO would be massive and significantly cheaper as the Threadripper Pro and Epyc chips sport a full 128 PCIe lanes which would remove the massive PCIe bridge chip on the current Mac Pro motherboard. In addition, AMD and Apple could have enabled Infinity Fabric links between the CPU and these GPUs. That's permit flat and fully coherent memory space between CPU and GPU memory pools. That hits the trifecta of more bandwidth, lower latency and improved efficiency. Bonus if AMD/Xilinx also released a FPGA accelerator card that also connected via Infinity Fabric.
While the professional applications on the Mac side of thing are generally written nowadays to expect multiple GPUs (the trash can model standardized that even though it was well... trash) I am always curious how these cards are exposed in Windows. CrossFire is long dead but this might be the weird exception due to the Infinity Fabric links: I'm curious how four Navi 21 chips working together handle gaming.