. Suppose an instruction takes 1/2 microsecond to execute (on the average), and a page fault takes 250 microseconds of processor time to handle plus 10 milliseconds of disk time to read in the page. (a) How many pages a second can the disk transfer? (b) Suppose that 1/3 of the pages are dirty. It takes two page transfers to replace a dirty page. Compute the average number of instructions between page fault that would cause the system to saturate the disk with page traffic, that is, for the disk to be busy all the time doing page transfers.