I think they are referring to the address space (from <a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;X86-64" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;X86-64</a>)<p>&gt; The AMD64 architecture defines a 64-bit virtual address format, of which the low-order 48 bits are used in current implementations.