Quiz 6, Q&A

Q. What is the notion of locality?

A. At a given time a process is only using a few pages or segments. For example, 90% of the memory portion is actually belongs to the 10% of the program. It is possible to guess the next page to bring the memory. The next page is possibly near in location to the page in the memory.

Q. What is “dirty bit”? Explain.

A. The Modified and Referenced bits keep track of the page usage. If the page in it has been modified, it must be written back to the disk. This bits sometimes called the dirty bit.

Q. Write the fit algorithms (memory search). Which one is the best? Why?

A. First-fit, Next-fit, Best-fit, Worst-fit. First-fit is to say the best since simulations show.

Q. What is the “present/absent bit”?

What happens when an executing program references an address that is not in main memory? The page table is extended with an extra bit, present/absent bit. Access to a page whose present bit is not set causes a special hardware trap, called page fault .