Addressability — 512GBytes is 2^39 bytes aka 2^36 8-byte chunks. So each memory address needs 39 bits, and each internal memory address bus needs either at leas

Addressability — 512GBytes is 2^39 bytes aka 2^36 8-byte chunks. So each memory address needs 39 bits, and each internal memory address bus needs either at least 36 or 39 wires, depending on the context — too much for 32-bit addresses. In other words, going to 7nm makes it easier to route wide busses around the chip. You could do the same thing on a larger process, but it's less space-efficient.