Chapter 8 (Virtual memory)

Question 1

What two characteristics lead to the memory management breakthrough?

Answer 1

All memory references are logical addresses translated at runtime

A process can be broken up into pieces and they need not be contiguous

Question 2

What is the portion of the process in main memory at a given time called?

Answer 2

Resident set

Question 3

What happens when something is referenced outside of the resident set?

Answer 3

Fault

Question 4

T/F Virtual memory can be larger than main memory

Answer 4

T

Question 5

What is it called when the OS may consume more CPU time managing the processes than running them

Answer 5

Thrashing

Question 6

What acts as an index into the page table?

Answer 6

Page number

Question 7

How do you get a physical address from a virtual address in paging?

Answer 7

Use the page number to index into the table. This gets the frame number which can be added to the offset to get the real address

Question 8

T/F A page table cannot be stored in virtual memory

Answer 8

F, it can

Question 9

What’s the drawback to an inverted page table?

Answer 9

The page number can no longer be used as an index into the page table

Question 10

What is a solution to the drawback of an inverted page table?

Answer 10

Hash function to map the virtual page number to a hash table. The hash table entry has a pointer to the frame table entry

Question 11

What’s the problem with virtual addresses?

Answer 11

Doubles the number of memory accesses

Question 12

What is TLB?

Answer 12

Translation Lookaside Buffer

Question 13

How can you help the virtual address problem of doubling the memory accesses?

Answer 13

Use a TLB

Question 14

T/F The TLB caches the pages

Answer 14

F, only the page table entries

Question 15

What is the “tag” for a cache block?

Answer 15

Leftmost bits of the address

Question 16

T/F A small page size increases internal fragmentation

Answer 16

F, reduces

Question 17

T/F As the page size grows, locality is strengthened and fewer faults will occur

Answer 17

F, locality is weakened and more faults will occur

Question 18

What is the page fault rate also determined by?

Answer 18

Number of frames allocated to a process

Question 19

List the benefits of segmentation

Answer 19

Ease of handling growing data structures

Modularity by assigning each module to a segment

Sharing and protection can be set per segment

Question 20

What is the fetch policy?

Answer 20

Determines when a page should be loaded into memory

Question 21

What are the two approaches to the fetch policy?

Answer 21

Demand paging

Prepaging

Question 22

What is the placement policy?

Answer 22

Where should a page be placed

Question 23

How can FIFO be improved?

Answer 23

Page buffering