Pages moving between RAM and virtual memory

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Quick Questions

Shade in the A or B circle for each question.

1. In paging, how is data divided up?

A Into variable-size files chosen by the user

B Into fixed-size blocks called pages

2. Which pages are moved out of RAM into virtual memory?

A Pages that are not currently needed (idle)

B Pages the CPU is using right now

3. The CPU needs a page that is stored in virtual memory. What happens?

A The page is swapped back into RAM

B The CPU runs the page directly from the hard drive

4. RAM is full and a new page is needed. What does the computer do first?

A Deletes the oldest page permanently

B Moves an idle page out to virtual memory to make room

5. Where is virtual memory located?

A On secondary storage, such as a hard drive or SSD

B Inside the CPU

Match the Pairs

Draw a line connecting each item on the left to its match on the right.

Left column		Right column
1page		Apaging
2swap out		BThe page must be swapped back into RAM before the CPU can use it
3A page the CPU needs is in virtual memory, so it is copied back into RAM		CMove an idle page from RAM to virtual memory to free up space
4Data is split into equal-sized blocks so it can be moved easily		DA fixed-size block of data that can be moved between RAM and virtual memory
5Pages are different sizes so they fit any gap in RAM		EPages are all the same fixed size, not different sizes
6The CPU runs a page straight from virtual memory		Fswap in

Definitions

paging

Fill in the Blanks

Complete each line of code by filling in the missing parts.

SWAP idlePage FROM RAM TO _____________

SWAP page2 FROM virtualMemory TO ___

IF page3Needed = TRUE ____ SWAP page3 FROM virtualMemory TO RAM ENDIF

numPages ← dataSize ___ pageSize

_____ ramFull = TRUE DO SWAP idlePage FROM RAM TO virtualMemory ENDWHILE

Spot the Error

Shade in the letter of the line that contains an error.

Question 1

A RAM ← [P1, P2, P3]

B idle ← P4

C MOVE idle FROM RAM TO VM

Question 2

A pageSize ← RANDOM(1, 9)

B pages ← CEIL(size / pageSize)

C OUTPUT pages

Question 3

A IF CPU needs page P5 THEN

B IF P5 is in VM THEN

C SWAP P5 OUT OF RAM

D ENDIF

E ENDIF

Question 4

A FOR each page in RAM

B IF page is in use THEN

C MOVE page TO VM

D ENDIF

E ENDFOR

Question 5

A RAM_FULL ← TRUE

B IF RAM_FULL = FALSE THEN

C MOVE idle page TO VM

D ENDIF

Answer Key

Pages moving between RAM and virtual memory

Section A: Quick Questions

B — Into fixed-size blocks called pages

A — Pages that are not currently needed (idle)

A — The page is swapped back into RAM

B — Moves an idle page out to virtual memory to make room

A — On secondary storage, such as a hard drive or SSD

Section B: Match the Pairs

page → A fixed-size block of data that can be moved between RAM and virtual memory

swap out → Move an idle page from RAM to virtual memory to free up space

A page the CPU needs is in virtual memory, so it is copied back into RAM → swap in

Data is split into equal-sized blocks so it can be moved easily → paging

Pages are different sizes so they fit any gap in RAM → Pages are all the same fixed size, not different sizes

The CPU runs a page straight from virtual memory → The page must be swapped back into RAM before the CPU can use it

Section C: Definitions

paging — Data is split into fixed-size pages. Idle pages are moved out of RAM into virtual memory, then swapped back into RAM when the CPU needs them.

Section D: Fill in the Blanks

SWAP idlePage FROM RAM TO virtualMemory

SWAP page2 FROM virtualMemory TO RAM

IF page3Needed = TRUE THEN
    SWAP page3 FROM virtualMemory TO RAM
ENDIF

numPages ← dataSize DIV pageSize

WHILE ramFull = TRUE DO
    SWAP idlePage FROM RAM TO virtualMemory
ENDWHILE

Section E: Spot the Error

B — The idle page must be one that is currently in RAM so it can be swapped out. P4 is not in RAM (RAM holds P1, P2 and P3). It should be a RAM page such as idle ← P2.

A — Pages are fixed-size blocks of data, so the page size must be a constant value such as 4096, not a random number.

C — The CPU needs P5 and it is in virtual memory, so it must be swapped INTO RAM. Swapping it out of RAM is the wrong direction.

B — Only idle pages (not currently needed) should be moved out to virtual memory. Moving pages that are in use would slow the program. It should be IF page is idle THEN.

B — Idle pages are moved to virtual memory to free space when RAM is full. The condition should be IF RAM_FULL THEN, not when RAM is not full.