Consider a segmented paging system with the segment table and the page table wit
ID: 3680274 • Letter: C
Question
Consider a segmented paging system with the segment table and the page table within a segment stored in memory. First part of the address is segment number, second part is the page number within a segment and the third part is the offset within a page. a) If a memory reference takes 200 nano seconds, how long does a segmented page memory reference take? b) If we add Translation Lookaside Buffer (TLB), and 80% of all memory references are found in the TLB, what is the effective memory reference time in each case? (Assume that finding a segmented page-table entry in the TLBs takes zero time, if the entry is there. Otherwise memory tables must be searched to determine the physical address. )
Explanation / Answer
a) It takes 400 nano seconds; it's two operations to get the word, one to find the page and one to find the segment within the page.
b) effective access time is
EAT =(1 – a) x memory access time + a ( 2*memoryaccess time + page fault overhead + swap page out + swap pagein + restart overhead)
this problem is not taking in account page this values: fault overhead, swap page out, swap pagein. restart overhead
therefore we take it like zero.
so
a =20%=0.2
EAT =(1 – a) x memory access time + a ( 2*memoryaccess time)
EAT=(0.8)*200ns+0.2*400ns=240ns