CS523 Operating Systems

1
CS523Operating Systems

• Fred Kuhns
• Applied Research Laboratory
• Computer Science
• Washington University

2
CS523 - Operating Systems

• Instructor Fred Kuhns
• Phone [phone]
• Email fredk_at_cs.wustl.edu
• Office Hours
• Tu/Th 400 - 500PM
• Location
• TBD
• Class times
• Tu/Th 230 - 400PM

3
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
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
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
Course Overview

• Overview of OS design issues
• Review of general purpose OS services
• Intro to Advanced OS Topics
• Real-Time, Database, Distributed and
  Multi-processor
• Detailed analysis of conventional OS internals
• Focus on UNIX - Linux, BSD, SVR4 and Mach
• Single/Multi-processor
• Resource management
• Focus on Real-Time design and implementation
• Performance and predictability issues
• Resource scheduling and managing concurrency

7
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
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
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
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
Layered Approach

• Simplifies design, implementation and testing
• Modular by dividing OS into functional layers.

environment
resource
HW
12
Kernel Based Approach

• Kernel contains a collection of primitives which
  are used to build the OS
• OS implements policy
• Kernel implements mechanisms

13
Virtual Machine Approach

• Virtual software layer over hardware
• Illusion of multiple instances of hardware
• Supports multiple instances of OSs

14

• 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
Types of Advanced OSs

• Distributed Operating Systems
• Multiprocessor Operating Systems
• Database Operating Systems
• Real-time Operating Systems

16
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
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
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
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
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
Traditional UNIX kernel

• Bloated kernel
• Inflexible supported single type of
• file system,
• process scheduling
• executable file format

22
Modern UNIX

• Separation of policy and mechanism
• modular design and implementation (layered)

23
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.