Here are some more details about x64 address limitation.
We've seen that in theory we can reach to the 64th power, which is
an enormous 16 EB of address space in theory, and that's an
unimaginable amount of memory or address space.
Now,
current CPU architectures only support 48 bits of addresses, and
this is how we get to these 256 TB, which is used as 128 TB per
process and 128 TB for the system.
So obviously there's lots of room to increase the address space size, but
currently most architectures are not supporting that. So we have 128 TB per
process and 128 TB for the system or kernel space.
However,
Intel, a few years ago is supporting, in fact, more than 48 bits, in
fact, they support 57 bits in the virtual address range using the
"Sunny Cove" Intel microarchitecture,
which is used by 9th and later generations of processors, and that gives us,
in theory, 64 PB per process and 64 PB for the system.
So currently Windows doesn't turn this feature on, in fact, Windows is already
built to support this kind of crazy big address space, but it's not turning on
this feature just because nobody currently can build such systems that have
any chance of being able to use that kind of memory, because you would need
lots of physical and page file memory in order for any process to get anywhere
near these kinds of numbers. But Windows is already ready to go, and at some point, I would guess that that feature would be turned on and used by systems.