1 - Memory Management

Question 1

If program A is loaded into memory starting at physical (real) address 1000 with logical (virtual) address 23, where is it bound?

Answer 1

1023

Question 2

What does a process consist of

Answer 2

Code, variables and constants

Question 3

Give Kibibytes in bytes

Answer 3

2^10

Question 4

Give Mebibytes in bytes

Answer 4

2^20

Question 5

Give Gibibytes in bytes

Answer 5

2^30

Question 6

Segmentation

Answer 6

Splitting a process up logically. Each segment has read, write and execute protection

Question 7

What is paging?

Answer 7

Paging splits process up into smaller size parts of equal size

Question 8

What is a page in real memory called?

Answer 8

Frame

Question 9

Pros and cons of pure paging

Answer 9

Poor Protection/sharing

Little wasted space

Question 10

What does a page table denote?

Answer 10

Where each of the process’ virtual pages are in main memory

Question 11

Demand Paging

Answer 11

Wait until a process makes reference to a page before loading.

upon page fault (page not in memory) load it rom backing store

Question 12

What is the valid-invalid bit?

Answer 12

Valid if page is in memory

Invalid if not

Question 13

What is page replacement?

Answer 13

When a free page is not available, use a page replacement algorithm to deicide victim frame to replace

Question 14

FIFO Page Replacement

Answer 14

First in First Out.

Simple queue of page age

Question 15

Modified Bit

Answer 15

Set to 1 when page is changed in main memory.

Speeds up replacement as only need to write to backing store if changed

Question 16

What is Thrashing?

Answer 16

Running processes are spending more time loading pages into memory than executing code

Reduce degree of multiprogramming to stop it

Question 17

Define working set

Answer 17

Set of pages accessed by a process in the past x ref

Each set being a locality

Question 18

Working Set Size

Answer 18

Tells us how many pages are in the WS of i (ie actively in use)

D <= m to avoid thrashing (m is total num of frames avail.)

Question 19

What is total demand?

Answer 19

D = WSS(i) where that is the sum of all processes working set sizes

Question 20

What is an inverted page table?

Answer 20

A table that reflects the state of the real memory

Find by using the pair (process_id, virtual page number)

Resort to process page table if virtual page not found in main memory

Question 21

What is Belady’s Anomaly?

Answer 21

More frames = more page faults in some ref strings