1. Fred Kuhns ( ) CS523S: Operating Systems
CS523
Operating Systems
Fred Kuhns
Applied Research Laboratory
Computer Science
Washington University

2. Fred Kuhns ( ) CS523S: Operating
CS523 - Operating Systems
• Instructor: Fred Kuhns
• Phone: 935-6598
• Email: fredk@cs.wustl.edu
• Office Hours:
Tu/Th: 4:00 - 5:00PM
• Location:
TBD
• Class times:
Tu/Th: 2:30 - 4:00PM

3. Fred Kuhns ( ) CS523S: Operating
Course Materials
• Textbook:
Real-Time Systems, Jane W. S. Liu
• Selected papers from the literature,
• Class handouts and presentation material,
• Class web page,
• OS man pages and web accessible
documentation,
• UNIX account.

4. Fred Kuhns ( ) CS523S: Operating
Programming Projects
• 3 projects plus a final project
• Final project:
 team/individual class presentations
 address a system issue covered in class. May build
on class projects. Report or implementation.
• Project focus:
 Correct, predictable behavior (of implementation)
 Performance (efficient execution)
 Completeness of design (address all issues)
 "readability" of code (can I understand it)

5. Fred Kuhns ( ) CS523S: Operating
Exams, Homework and Grading
• Weekly: Homework assignment or Quiz
• Final Exam (no mid-term):
Comprehensive
• Relative weights:
25% Final exam
20% Quizzes
10% Homework
30% Programming projects (10% per project)
15% Final Project

6. Fred Kuhns ( ) CS523S: Operating
Course Overview
Overview of OS design issues
o Review of general purpose OS services
o Intro to Advanced OS Topics:
• Real-Time, Database, Distributed and Multi-processor
Detailed analysis of conventional OS internals:
o Focus on UNIX - Linux, BSD, SVR4 and Mach
o Single/Multi-processor
o Resource management
Focus on Real-Time: design and implementation
o Performance and predictability issues
o Resource scheduling and managing concurrency

7. Fred Kuhns ( ) CS523S: Operating
Introduction
• Functions of an Operating System
Resource management
User environment
• Design Approaches
Layered, Kernel and Virtual
• Types of Advanced Operating Systems
Distributed, Multiprocessor, Database and Real-time
• Overview of UNIX (why do we care)

8. Fred Kuhns ( ) CS523S: Operating
Functions of an OS
• Resource Management
Time management - temporal properties
CPU and disk transfer scheduling
Space management
main and secondary storage allocation
Synchronization and deadlock handling
c
Accounting and status information
s

9. Fred Kuhns ( ) CS523S: Operating
Functions of an OS (cont)
• User Environment - OS layer transforms bare
hardware machine into higher level abstractions
Execution environment - process management, file
manipulation, interrupt handling, I/O operations,
language.
Error detection and handling
Protection and security
Fault tolerance and failure recovery

10. Fred Kuhns ( ) CS523S: Operating
Design Approaches
• Deal with complexities of modern systems
• Separation of Policies and Mechanisms
Policies - What should be done
Mechanisms - How it should be done
Levin, R., E. Cohen, W. Corwin, F. Pollack and W. Wulf,
"Policy/Mechanism Separation in HYDRA," Proceedings
of the 5th
Symposium on Principles of Operating Systems,
1975, pp. 132-140.
• Three common approaches:
Layered Approach
Kernel Approach
Virtual Machine Approach

11. Fred Kuhns ( ) CS523S: Operating
Layered Approach
Level Name Objects Example
13 Shell User programming env. Bash statements
12 User process User process Quit,kill,suspend,resume
11 Directories Directories Create,destroy,attach,list
10 Devices External: printer,display Create,open,close
9 File system Files Create,open,close
8 Communications Pipes Crreate,open,close
7 Virtual memory Segments,pages Read,write,fetch
6 Local secondary store Blocks,channel Read,write,fetch
5 Primitive process Process,semaphore Suspend,resume,wait
4 Interrupts Interrupt-handlers Invoke,mask,retry
3 Procedures Procedure,stack,display Mark stack,call,return
2 Instruction set Evaluation stack Load,store,add
1 Electronic circuit Registers,gates,buses Clear,transfer,activate
Simplifies design, implementation and testing
Modular by dividing OS into functional layers.
HWresourceenvironment

12. Fred Kuhns ( ) CS523S: Operating
Kernel Based Approach
Kernel contains a collection of primitives
which are used to build the OS
OS implements policy
Kernel implements mechanisms
Hardware
kernel
Operating system

13. Fred Kuhns ( ) CS523S: Operating
Virtual Machine Approach
Virtual software layer over hardware
Illusion of multiple instances of hardware
Supports multiple instances of OSs
Hardware
Virtual machine software
VM1 VM2 VM3 VM4

14. Fred Kuhns ( ) CS523S: Operating
• Layered:
Dijkstra, E. W., "The Structure of THE Multiprogramming
System", Communications of the ACM, May 1968, pp. 341-346.
• Layered (Ring):
Organick, E., The Multics System, MIT Press, Cambridge, MA.
1972.
• Kernel
Brinch Hansen, P., "The Nucleus of a Multiprogramming
System", Communications of the ACM, Apr. 1970, pp. 238-241.
Wulf, W., E. Cohen, W. Corwin, A. Jones, R. Levin, C. Pierson,
and F. Pollack, "HYDRA: The Kernel of a Multiprocessor
Operating System", Communications of the ACM, June 1974,
pp. 337-345.
• Virtual
Seawright, L., and R. MacKinnon, "VM/370 - A Study of
Multiplicity and Usefulness", IBM Systems Journal, 1979, pp.
4-17.

15. Fred Kuhns ( ) CS523S: Operating
Types of Advanced OSs
Distributed Operating Systems
Multiprocessor Operating Systems
Database Operating Systems
Real-time Operating Systems

16. Fred Kuhns ( ) CS523S: Operating
Distributed Operating Systems
• Controls and manages resources for a network of
autonomous computers
manage both hardware and software resources
behaves as a single monolithic system.
• User not aware of program or resource location
• Design issues same as traditional systems
• Practical issues:
lack of shared memory
lack of global clock
unpredictable communication delays.

17. Fred Kuhns ( ) CS523S: Operating
Multiprocessor Operating Systems
• Consists of a set of processors that
share a set of physical memory blocks
share a common clock
"share" over an interconnection network.
• Control and manage resources
hardware and software resources
viewed as a uniprocessor system.
• Design issues same as traditional system.
• Practical issues:
increased complexity of synchronization, scheduling,
memory management, protection and security.

18. Fred Kuhns ( ) CS523S: Operating
Database Operating Systems
• Database systems place increased demands on an
operating system to efficiently support:
concept of a transactions
manage large volumes of data
concurrency control
system failure control

19. Fred Kuhns ( ) CS523S: Operating
Real-time Operating Systems
• Place application specific special requirements
on an operating system.
• Policies and mechanisms are geared to
ensuring jobs meet their deadlines.
• Problem is one of resource scheduling and
overall system utilization.

20. Fred Kuhns ( ) CS523S: Operating
Why UNIX
• Historical significance
• Advanced features developed for or ported to
UNIX
• Availability of source code and research papers
• Importance to present and future research
activities at WashU
• Highlights key design and architectural issues

21. Fred Kuhns ( ) CS523S: Operating
Traditional UNIX kernel
• Bloated kernel
• Inflexible: supported single type of
file system,
process scheduling
executable file format
file
system
virtual
memory
loader
block dev char dev
kernel

22. Fred Kuhns ( ) CS523S: Operating
Modern UNIX
• Separation of policy and mechanism
• modular design and implementation (layered)
AcrobatDocum ent

23. Fred Kuhns ( ) CS523S: Operating
References
• Original UNIX implementation:
D. M. Ritchie, and K. Thompson, “The UNIX
Time-Sharing System”, Communications of the
ACM, Vol. 17, No. 7, Jul. 1974, pp. 365-375.