Question

Consider the following page reference string for a three-frame memory: 

6 3 1 5 3 4 3 2 5 4 3 4 5 1 5 3 1 6 3 1

Apply LRU, Clock and FIFO algorithms


What will be the number of page faults for each replacement algorithm  note that page faults at the beginning are counted?

Answer 1

① LRO Algorithm. Replace page the which is not used for longest time! 1 - 0 12 16 63115 34 32 54 3.4.5.153 31 51212 2 66 65.55 3 331 3 3 3 3 3 3 3 3 3 4 4 4 4 4 4 33 313 6 51515151515 15 616 14.414155 II 1 X 1 X 11 | x x x x x x 3 1 Total fault hit page page 12 8. Total

bit o.. same page comes In clock algorithm, we have to set reference bit. Reference bit may be oorl When page comes first it has reference When the same second reference bit set to l. page is not replaced if reference bit is 1. That page has given second chance. for Remaining pages apply fifo In example, I have shown reference bits before numbers as or 1

@ Clock Algorithm Take reference bit for o or I page 6 1 4. O 0 O 0 3 6 3 6 2104 5 5. 3 o 06 3 3 5 3 & 5 3 4 1 3 2 5 2 3 3 4 X. I Gwinn 13 5 lo 0 6 0 10 1 - X 1 - IM ·3 S 6 1 5 3 05 O 0 0 € 0 0 4 4 3 0 5 4 3 لا احیا 3 3 13 13 0 6 2 2 3 05 0 06 0 3 1 Х Х 4 3 5 Х Total Total 1 Х 6 X XI page Fault = 12 page Hit = 8

(3 FIFO Algorithm oldest page is replaced for for replacement 6 3 15 34 3 2 54 3.4.5.1 53.16 3:1 016665555 212 213131313 31 33666 3 3 3 3 4 4 455555 lili 3 3 1111131313 141414 414 1515151515 Ixil I XXII XXIII - 15 Total Total page fault hit page