48 bits lets you have 256 terabytes of addressable memory. If you go to 56 bits, you get ~64 petabytes of addressable memory. 48 bits is probably good for 5-10

48 bits lets you have 256 terabytes of addressable memory. If you go to 56 bits, you get ~64 petabytes of addressable memory. 48 bits is probably good for 5-10 years as we hit the limits of process shrinks. 56 bits should be good for a quite a bit longer. This is all assuming we don't find some magical memory tech that lets us add orders of magnitude more memory without needing absurd amounts of cooling and power.