[whaleofatw2022]

IIRC Apple is using the lower channel width options in LPDDR5.

I.e. instead of 64 bit channels they do 16 (or maybe 32) bit. That lowers the die area needed on the chip for memory controllers.

But it also impacts bandwidth, AFAIK an M4 ultra is still on the order of 1/4 the bandwidth of something like a 5090