Question on Virtual memory and Physical memory
The page entry contains other things than the base of the physical page.  Typically:


a present or absent bit (to handle the case where the page is not present in the memory: is on disk or just does not exist)
access right: may the process read, write, execute the page
some kind of use count (to help the OS makes its choice when there is a need page out)


and obviously some bits may be unused or reserved for future usage.

Note that, although in 64-bit system we are in a phase where the virtual address space is bigger than the physical address space, historically on architectures which lived long enough that tends to be followed by a phase where the physical address space is bigger than the virtual one.  The additional memory may be visible only by the OS (which will put other processes there), or even made available to user processes with some kind of bank switching (see extended and expanded memory or more recently PAE in x86 world, some other architectures have had similar things)