self doubt

Question

Consider a paging system with a page table stored in memory where memory reference takes 200 nanoseconds and all pages are in memory.

If we add associative registers (TLB), and 75% of all page-table references are found in the associative registers, what is the effective memory reference time on average? (Assume that finding a page table entry in the associative registers takes 10 nanoseconds, if the entry is there.)

What is the effective memory reference time if the hit ratio for the associative registers 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, etc takes 100 m seconds.)

Comments

but why 2 hit ratios for TLB?

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two diff. questions

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(a) 10ns+200ns+0.25*200ns=260ns