My favorite part of SGI computers, like Altix and UV lines, was the NUMA memory with flexible interconnect. NUMA let you program a pile of CPU’s more like a single-node, multithreaded system. Then, the flexibility let you plug in CPU’s, graphics cards, or FPGA’s. That’s right into the low-latency, high-speed, memory bus.
There was a company that made a card that connected AMD servers like that. I don’t know if such tech ever got down to commodity price points. If you had Infiniband, there were also Distributed, Shared Memory (DSM) libraries that simulated such machines on clusters. Data locality was even more important then, though.
Cray XT/SeaStar? iirc the interconnect ASIC pretends to be another peer CPU connected via HyperTransport. HPE Flex is similar, but works via QPI/UPI for Intel CPUs.
There was a company that made a card that connected AMD servers like that. I don’t know if such tech ever got down to commodity price points. If you had Infiniband, there were also Distributed, Shared Memory (DSM) libraries that simulated such machines on clusters. Data locality was even more important then, though.