Right. With 64-bit ISAs you can address 2^64 bytes, but... you can't exactly have 2^64 bytes. At some point the system will fail. How it fails is important.

Right. With 64-bit ISAs you can address 2^64 bytes, but... you can't exactly have 2^64 bytes. At some point the system will fail. How it fails is important. A ran-out-of-resources errors is a lot better than undefined behavior resulting from random memory corruption. And yes, portable C has finite size_t. Therefore portable C must fail in some way when limits are exceeded.