There are different implementations of page tables, but they usually contain the following:

1. A present/absent bit which is 1 if this page is currently loaded in a frame
2. A dirty bit which tells if this page differs from its disk copy
3. The physical frame number if this page is currently in a frame
4. The disk address of this page, telling where to find the permanent copy
5. A timestamp, telling the last time this page was accessed.

If the page is not currently in physical memory, then the dirty bit is ignored and the physical frame number is invalid. Only the disk address matters. If the page is in a frame of physical memory, then all the fields are valid.