chapter 44 - flash based SSDs

Question 1

What are the basic structural units in flash memory?

Answer 1

pages → blocks → banks

Pages are the smallest read/write unit

Question 2

What are the three fundamental operations in flash memory?

Answer 2

Read (fast), Program (1→0 only), Erase (resets entire block to 1s, slow)

Question 3

Why can’t you overwrite a programmed page in flash memory?

Answer 3

You can’t change 0s back to 1s—must erase the whole block first

Question 4

What is the role of the Flash Translation Layer (FTL)?

Answer 4

Translates logical block addresses to physical flash pages

manages read/program/erase operations

Question 5

What’s the main drawback of a direct-mapped FTL?

Answer 5

poor performance due to frequent block erases

Question 6

What is the key idea behind a log-structured FTL?

Answer 6

Always write to the next free page and use a mapping table to track logical→physical locations

Question 7

What causes garbage accumulation in SSDs?

Answer 7

old data that is overwriten - garbage

Question 8

What is wear leveling?

Answer 8

spread out write and erase operations evenly,

so no single block wears out too quickly

Question 9

Difference between passive and active wear leveling?

Answer 9

Passive - moves rarely changed data blocks to high-wear blocks

active - spreads out new writes across blocks that have been erased the fewest times