After reading about wafer scale, I found this other new type of processor:

The Bow IPU is the first processor in the world to use Wafer-on-Wafer (WoW) 3D stacking technology, taking the proven benefits of the IPU to the next level.

An IPU is an “Intelligence Processing Unit”. With the boom of AI/ML, we have a new word.

There is a paper about it, from 2019, but still interesting. I haven’t been able to read fully and understand it but the section 1.2 about the differences between CPU, GPU and IPU helps to see (very high level) how each one works.

CPU: Tends to offer complex cores in relatively small counts. Excel at single-thread performance and control-dominated code, possibly at the expense of energy efficiency and aggregate arithmetic throughput per area of silicon.

GPU: Features smaller cores in a significantly higher count per
device (e.g., thousands). GPU cores are architecturally simpler. Excel at regular, dense, numerical, data-flow-dominated workloads that naturally lead to coalesced accesses and a coherent control flow.

IPU: Provides large core counts (1,216 per processor) and offer cores complex enough to be capable of executing completely distinct programs. IPU only offers small, distributed memories that are local and tightly coupled to each core. And are implemented as SRAM.

From a pure networking view, their pod solution uses 100G RoCEv2. So no infiniband.

In general, all this goes beyond my knowledge but still interesting the advances in processor technology with “wafer” likes design. It seems everything was focused in CPU (adding more cores, etc) and GPU. But there are new options, although the applications looks very niche.