Virtual Memory

Question 1

what is fetch policy?

Answer 1

a decision on when to load something into memory

Question 2

what is placement policy?

Answer 2

a decision on where to load something into memory

Question 3

what is replacement policy?

Answer 3

a decision on which part of something in memory to replace

Question 4

What is effective memory access time? The concept, not the equation.

Answer 4

basically, the OS uses a page table to look up the page IDs for the pages it needs to reference. This table has page IDs and their corresponding addresses in memory

The OS system is able to cache some of those pages (pages it believes will be used the most frequently) in registers for quick lookup (a successful lookup is called a cache hit).

If the pageID that it’s looking for is not in cache (a cache miss), it will have to make 1 RAM access to look up the page table for the ID and then another RAM access to actually retrieve the page.

Since some percentage of the time there will be cache misses, then the average access time experienced by the user will always be greater than the time it takes to make 1 RAM access. This average is called the effective memory access time

Question 5

effective memory access time equation

Answer 5

(1-p) * RAM access time + p(pf service time + RAM access time)

where p is the page fault rate