That would make usize a 32-bit integer, regardless of the data width. It does make other hidden assumptions though, such as that there is a single "memory" tha

That would make usize a 32-bit integer, regardless of the data width. It does make other hidden assumptions though, such as that there is a single "memory" that is uniquely identified by a usize value, regardless of the way it is accessed. For x86, for example, the same address could either refer to a location in memory or to a location in an I/O device, depending on whether in/out instructions or "normal" instructions were used.