Solution to Problem 1
The dirty bit(modify bit) plays a good role Associate with every memory's frame a dirty bit and set it to 0. Whenever the contents of the frame is modified(via an instruction that stores something), then set the dirty bit to 1 If the dirty bit for a particular frame is 1, then swap it out to disk Otherwise, no need to swap it out to disk, and the OS saves a lot of time(because disk access is mechanical and thus very time consuming)