Virtual Memory

Question 1

Explain a multi-level page table address

Answer 1

(outer page number)(inner page number)(offset)

Question 2

What is internal fragmentation?

Answer 2

When we have unused portions of memory that have been allocated because the page size was too large for its needs

Question 3

What are the pros/cons of smaller/larger page sizes?

Answer 3

Smaller pages ==> larger page table

Larger pages ==> smaller page table, but more internal fragmentation

Question 4

What is a TLB and why do we need it?

Answer 4

Translation Look-Aside Buffer. Because the page table is stored in memory, we must do a memory access to translate a VA->PA ==> very slow ==> use TLB

Question 5

What happens on a TLB miss?

Answer 5

1. Software TLB Miss handling - control goes to OS to find the correct page table(s) and translation (embedded)
2. Hardware TLB miss handling - processor finds the correct translation by accessing tables directly

Question 6

Properties of a TLB

Answer 6

• Smaller and therefore faster than the cache
• Can store exact translation
• Usually fully or highly associative
• 64 - 512 entries
• Can have an L1 and L2