In our presentation so far, the page-fault rate is not a serious problem, since each page is faulted for at most one, when it is first referenced. This representation is not strictly accurate. Consider that. If process of 10 pages actually uses only one-half of them, then demand paging saves the I/O necessary to load the five pages that are never used. We could also increase our degree of multiprogramming by running twice as many processes. Thus, if we had 40 frames, we could run eight processes, rather than the four that could run if each required 10 frames (five of which were never used).