Lecture 0x10

Lecture 0x10: Virtual Memory
Date: Monday, November 10, 2025

Agenda

Announcements
- The next readings/activities from OS zyBook
  - Chapter 18, due after Exam 2, Friday, November 21
- Programming Project 4: Basic Shell [HTML] [PDF] due tonight
- Lab 7: Interprocess Communication [HTML] [PDF] due Wednesday night
- Programming Project 5: Roger Bacon Shell with Pipes and Redirection [HTML] [PDF] parsing functionality due November 21
LRU approximation algorithms
- Second-chance or Clock Algorithm uses one reference bit and a clock pointer, treating the frames of memory as a circular array
- Gold's Clock Algorithm/third-chance also considers a "dirty" bit to try to avoid selecing pages that need to be written back to disk because they are more expensive
Counting algorithms
- Least-frequently used (LFU)
- Most-frequently used (MFU)
- not obvious why or when these are useful - something to think about
- direct implementations may suffer from same overhead costs as a direct implementation of LRU
Looking at the exercises for OS zyBook Chapter 16, Sections 2-4
- Revisiting 16.1.3
- 16.2.3, 16.2.4
- 16.3.1, 16.3.2
- 16.4.1
Lab/Project time

Terminology