Invalid page fault :If a page fault happens for a reference to an address that's not part of the virtual address space, so that there could not be a page in memory corresponding to it, then it is named an invalid page fault. The page fault handler in the operating system then requires ending the code that made the reference, or give an indication to that code that the reference was not valid. A null pointer is generally represented as a pointer to address 0 in the address space; various operating systems set up the memory management unit to show that the page that have that address is not in memory, and do not add that page in the virtual address space, so that attempts to write or read the memory referenced by a null pointer have an invalid page fault.