CS703 – Advanced Operating Systems Assignment No.3 solution January 2016

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Question 1 Marks 25
Consider a paging system with a page table stored in memory.
(a) Marks 5
If a memory reference takes 200 nanoseconds, how long does a paged reference take
(reference is retrieved from page table in memory and then program data is retrieved
from memory) Assume all pages are in memory?
(b) Marks 10
If we add a Translation Look-aside Buffer (TLB), and 75 percent of all page-table
references are found in the TLB i.e. the TLB hit ratio is 75%, what is the effective
memory reference time on average? (Assume that finding a page table entry in TLB takes
10 nanoseconds, if the entry is there.) Assume all pages are in memory.
© Marks 10
What is the effective memory reference time if the hit ratio for TLB is 70%, the hit ratio
for memory is 20%, and 10% of the time we must go out to the disk to load the faulted
page in memory, where context switching, disk transfer time takes 100 m seconds