Memory
Physical and Virtual
Prof. Sirer
CS 316
Cornell University
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
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?


0x7fffffff
Stack
Processor
Heap
Data
0x1000
Text
e.g. 0x000000000 ?
uninitialized pointer
Memory
Physical Addressing Problems
What happens when
another program is
executed concurrently on
another processor?

0x7fffffff
Stack
Stack
The addresses will conflict
Heap
Heap
We could try to relocate
the second program to
another location

Assuming there is one

Introduces more problems!
Data
Data
Processors
0x1000
Text
Text
Memory
Physical Addressing Problems
What happens when
another program is
executed concurrently on
another processor?

Stack
0x7fffffff
Stack
Heap
The addresses will conflict
Data
We could try to relocate
the second program to
another location

Assuming there is one

Introduces more problems!
0x4000
Text
Heap
Processors
Data
0x1000
Text
Memory
Protection
Memory accesses can be confined with the
aid of some simple hardware

Segmented architectures

Page tables
 Single-level
 Multi-level
 Inverted

TLBs