1. Memory Physical and Virtual
Prof. Sirer
CS 316
Cornell University

2. System Organization Recap
We have covered the principles of processor design
Can execute a program, efficiently
We have covered the bare essentials of memory organization
Can store program instructions and data
Time to look at advanced issues and generalize our computer system
Isolation
Protection
Virtualization

3. Processor & Memory
Currently, the processor’s address lines are directly routed via the system bus to the memory banks
Simple, fast
What happens when the program issues a load or store to an invalid location?
e.g. 0x ?
uninitialized pointer
0x7fffffff
Stack
Processor
Heap
Data
Text
0x1000
Memory

4. Physical Addressing Problems
What happens when another program is executed concurrently on another processor?
The addresses will conflict
We could try to relocate the second program to another location
Assuming there is one
Introduces more problems!
0x7fffffff
Stack
Stack
Heap
Heap
Data
Data
Text
Text
Processors
0x1000
Memory

5. Physical Addressing Problems
What happens when another program is executed concurrently on another processor?
The addresses will conflict
We could try to relocate the second program to another location
Assuming there is one
Introduces more problems!
Stack
0x7fffffff
Stack
Heap
Data
Text
0x4000
Heap
Processors
Data
Text
0x1000
Memory

6. Protection
Memory accesses can be confined with the aid of some simple hardware
Segmented architectures
Page tables
Single-level
Multi-level
Inverted
TLBs