1 Memory Systems Virtual Memory Lecture 25 Digital Design and Computer Architecture Harris & Harris Morgan Kaufmann / Elsevier, 2007

2 But First…

3 The Memory Hierarchy

4 The Hard Disk

5 Virtual Memory Overview Physical Memory acts as a cache for virtual memory. Page table maps virtual pages to physical pages. This mapping of virtual addresses to physical addresses is called address translation. Translation Lookaside Buffers (TLBs) speed up address translation.

6 Virtual and Physical Addresses

7 Cache/Virtual Memory Analogues CacheVirtual Memory BlockPage Block SizePage Size Block OffsetPage Offset MissPage Fault Tag Virtual Page Number

8 Virtual Address Translation

9

10 The Page Table

11 Replacement Policies

12 Translation Lookaside Buffer (TLB)

13 Example TLB

14 Virtual Memory

15 Memory System Summary