Question

III. Consider a process that has been allocated 5 pages of memory: P1, P2, P3, P4, and P5.
The process accesses these pages in the following order:
P1 P2 P3 P4 P1 P2 P5 P1 P2 P3 P4 P5

(i) Illustrate Belady’s anomaly by precisely describing the execution of the FIFO page
eviction algorithm in two cases:

a) where the machine has 3 pages of physical memory, and
b) where the machine has 4 pages of physical memory, and by comparing the number of page
faults incurred in these two cases. (When the process begins executing, none of its pages are
present in memory.) (2 points)

(ii) Show how the LRU page eviction algorithm would work in the same scenarios a) and b)
described above. (2 points)

Answer 1

Eelody's anomaly: eladys anomly is it the number of- fyames are incyease en ennumbes pa aults ae ala0 increase. Notes → In some -times ot Ye ve Y page faul h - hit(page hit) FIFO るframes 6 Pl

Beladys' anomaly: If we increase frames of memory than page faults also increases.

in the above example when 3 frames in memory we get 9 page faults. But in the case of increased 4 frames page faults are increased .so FIFO follows Belady's anomaly

LRO (Least recenty wed) fault:8 page 10 4 frames page faults 8 anamoly is only wok foy FIFo

mostly Belady’s anomaly is used for FIFO only. In case of LRU when 3 frames we get 10 pagefaults but in case of 4 frames we get 8 page faults it is oppostie to Belady's anomaly.