CMSC 421: Exam 4(Complete solutions)

Virtual memory correct answers a collection of one or more logical address spaces, each of which may exceed the size of physical memory Logical address correct answers referred to as virtual address Demand paging correct answers principle of loading a page into memory only when the page is needed, rather than at the start of the execution Present bit correct answers binary flag in each page table entry that indicates whether the corresponding page is currently resident in memory If a page is resident in memory... correct answers the entry points to the frame that holds the page Page fault correct answers an interrupt that occurs when a program attempts to reference a non-resident page When a page fault occurs... correct answers the interrupt triggers the operating system to find the page on disk, copy the page into a frame, and set the present bit to 1 Reference string correct answers is the sequence of page numbers referenced by an executing program during a given time interval Reference strings are used to compare... by... correct answers 1) different page replacement algorithms 2) counting the number of page faults generated Optimal Page Replacement Algorithm correct answers selects the page that will not be referenced for the longest time in the future The... algorithm is guaranteed to... correct answers 1) optimal page replacement algorithm 2) generate the smallest number of page faults for any reference string The... algorithm... is... correct answers 1) optimal page replacement algorithm 2) unrealizable FIFO page replacement algorithm correct answers throws out the oldest page Least-recently-used page replacement algorithm (LRU) correct answers selects the page that has not been referenced for the longest time Referenced bit (r-bit) correct answers is a bit associated with a page and is set automatically by the hardware whenever the page is referenced by any instruction