A64fx have on board HMB -> that means no dram. If you look at the fugaku mother board their is no Dimm slots. All the memory is on the same package as the CPU.

This delivers a huge boost in bandwith.

HMB stand for high memory bandwidth. It offers up to 900 GB/s.

Now if you add the tofu interconnect on top you have a systems finely tuned for maximising data movement.

Remember : compute is cheap, communication is expensive.

You can have load of gpu and processors but if you can't feed them data fast enough they are useless.