The industry has a long history of machines whose "bit width" did not match their maximum physical address size. For example, the VAX architecture defines a 32-bit machine, and virtual addresses (which are the addresses used by code once address translation is turned on) are indeed 32 bits wide... but the VAX's physical addresses are only 30 bits wide - and half of the physical address space is devoted to I/O device registers, so maximum RAM was only 512 MiB.