Frequently, on a 32-bit CPU, each page-table entry is 4 bytes long, but that size can vary as well.
A 32-bit entry can point to one of $2^{32}$ physical page frames.
If frame size is 4 KB (212), then a system with 4-byte entries can address $2^{44}$ bytes (or 16 TB) of physical memory.
The above statement is taken from the book "Operating System Principles" by Galvin.
If all 32 bits in a 32-bit CPU are used to refer to pages , then we can have $2^{32}$ pages. But then no more bits will be left to point to memory inside a page of size $2^{12}$ bits since all 32-bits have been used up.
How can we thus say that $2^{44}$ bytes are addressable?