Q. What is the effect of permitting two entries in a page table to point to the same page frame in memory? Describe how this effect could be used to decrease the amount of time needed to copy a large amount of memory from one place to another. What effect would updating a few byte on the one page have on the other page?
Answer: By permitting two entries in a page table to point to the same page frame in memory users can share code and data. If the code is re-entrant a lot memory space can be saved through the shared use of large programs such as text editors and compilers and database systems. Copying large amounts of memory could be consequence by having different page tables point to the same memory location.
Nevertheless sharing of non-re-entrant code or data means that any user having access to the code can modify it and these modifications would be reflected in the other user's copy.