- This document outlines the syllabus for the CSC 369H1F Operating Systems course in Fall 2012. - It introduces the course objectives, assignments, exams, topics to be covered, and expectations for workload. Students will complete code reading, programming, and design document assignments on the OS/161 simulated operating system. - The first lecture provides an overview of operating systems and their role in managing computer resources and coordinating hardware and software components. It discusses the goals of convenience and efficiency for users and the system.

1. CSC 369H1F, Fall 2012 Lecture 1
Administrivia
CSC 369H1F • Instructor Contact:
• Email: demke@cs.toronto.edu
• Office: BA 5228
• Office Hours: Wed 2-3 p.m., Fri 10-11 a.m. (may change)
• Webpage:
Operating Systems • http://www.cdf.toronto.edu/~csc369h/fall/
Fall 2012 • Calendar:
Professor Angela Demke Brown • Check it carefully – some lectures may be in tutorial time!
U of T • Bboard:
• Will be linked from course webpage, not yet available
• Course Info Sheet (due dates, policies, etc.):
• Linked from course webpage
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Course Overview Assignments (40%)
• Objectives: • Code Reading component:
• To understand the role of the OS, • Questions about the code we give you
• To become familiar with the major subsystems of a • Reinforce lecture concepts, familiarize you with the
modern OS, and the design principles and code before you start writing
implementations behind them; • Programming component
• To understand benefits and dangers of concurrency • Language for this course is C
• How are we going to get there? • Correctness and performance considerations
• Lectures, textbook readings, handouts • Design Document component
• Tutorial sections (discussion, review, questions, etc.) • Think about what you need to build first
• Simulated OS development project (OS/161) • Tell us in plain English what you were thinking.
• Tell us how to find your code.
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2. CSC 369H1F, Fall 2012 Lecture 1
Workload Don’t Panic!
• This course is very work-intensive • Help is available in many forms
• Lectures cover a lot of new concepts • Your partner(s): Work together
• Many of these are very abstract
• Only way to really understand how it works is to try
• Lectures/tutorials: Ask questions!
doing it yourself • Office hours: My time dedicated specifically to
• Assignments build on a realistic OS helping you
• There is a lot of existing code given to you • Discussion board: Fast response!
• You should not expect to understand all of it
• Email: Longer turnaround time
• You should be comfortable with prereq material
• Unix tools (svn, debugger, scripts) • Anonymous email: for feedback
• Computer organization, memory model, etc.
• C programming (especially pointers!)
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Don’t Copy! Exams
• Academic Dishonesty: Plagiarism and cheating • Midterm (20%)
• Very serious academic offences • Thursday, Oct 25th, in tutorial time (end of Week 7)
• Please don’t. It’s painful for everyone. • Covers material up to end of Week 6
• Can discuss OS161, tools, concepts with your • Final (40%), 40% required to pass
classmates • Will be scheduled by Arts & Sciences
• Can discuss solutions to the assignments only with your • Will be cumulative
partner(s), the TA, or the instructor
• I will be explicit about what you are responsible for
• there is a clear distinction between collaboration on the final
and cheating.
• Lots of final exams from 369 are available for study
• Ask questions on the bboard, but don’t add details
about your solution
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3. CSC 369H1F, Fall 2012 Lecture 1
Course Content Introduction
• List of topics, in order: • Read Chapter 1
• Introduction (Today) • Some (much?) of this should be review
• Processes and Threads
• Concurrency and Synchronization • What is an OS and why do I want one?
• CPU Scheduling • How does it relate to the other parts of a computer
• Memory Management system?
• File and I/O Systems • Review some computer organization and C concepts
• Security
• Deadlock • What are the major parts of an OS?
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Roles of the OS Goals of the OS
• An OS is a resource allocator • Primary: convenience for the user
• allows the proper use of resources (hardware, software, data) in • it must be easier to compute with the OS than without
the operation of the computer system it
• provides an environment within which other programs can do
useful work • Secondary: efficient operation of the computer system
• An OS is a control program
• controls the execution of user programs to prevent errors and • The two goals are sometimes contradictory
improper use of the computer • Actually, often contradictory
• especially concerned with the operation and control of I/O • Which goal takes precedence depends on the purpose of the
devices computer system
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4. CSC 369H1F, Fall 2012 Lecture 1
What Impacts OS Design? Overview of Computer System
• On one hand, its goals User App User App User App User App User App User App
• Convenience Operating System
Memory
• Efficiency and speed Synchronization Scheduling File System Networking
Mgmt
OS Machine Dependent Code
Hardware
• On the other hand, practical constraints CPU
• What do applications need?
Memory Bus I/O Bridge
• What does the hardware provide?
I/O Bus
Main
• The constraints keep changing! Memory
Disk Display Ethernet
Controller Controller Controller
• So OS keeps changing too
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Storage Structure Storage Hierarchy
• Main memory (DRAM) stores programs and data • processor registers, main memory, and auxiliary memory
during program execution form a rudimentary memory hierarchy
• DRAM cannot store these permanently because it is too • the hierarchy can be classified according to memory
small & it is a volatile storage device speed, cost, and volatility
• auxiliary memory: hold large quantities of data • caches can be installed to hide performance differences
(including programs) permanently when there is a large access-time gap between two levels
• Main memory is only storage (other than
registers) CPU can access directly
CPU Main Memory
• Forms a large array of bytes (1 byte = 8 bits) of L2/L3
memory, each with its own address L1 Cache Disk
Cache Tape
• we say that main memory is byte-addressable
Larger, slower, cheaper
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5. CSC 369H1F, Fall 2012 Lecture 1
Hardware Support for OSs Protection Domains
• Protection domains -> mode bit • Dual-mode operation: user mode and system mode (a.k.a
supervisor mode, monitor mode, or privileged mode)
• Interrupts
• Intel actually has 4 “rings” for protection
• Timers • Add a mode bit to the hardware and designate some
• Memory Management unit instructions as privileged instructions
• Attempting to execute privileged instruction from user mode
• Other hardware causes protection fault  trap to OS
• Protects the operating system from access by user programs,
and protects user programs from each other
• What instructions/operations would you expect to be
privileged?
 Setting mode bit? Writing to device registers?
 Disabling interrupts?  Performing DMA?
Enabling interrupts?  Halting the CPU?
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Interrupts Interrupts
• An interrupt is a signal that causes the CPU to jump to a • An interrupt is a signal that causes the CPU to jump to a
pre-defined instruction called the interrupt handler pre-defined instruction called the interrupt handler
• May be caused by software or hardware • May be caused by software or hardware
CPU 1. OS fills in Interrupt CPU 4. CPU changes mode,
Fetch Decode Execute Table (at boot time) Fetch Decode Execute disables interrupts
2. CPU execution loop: 5. Interrupted PC value
IDTR User PC OldPC fetch instruction at IDTR Kernel PC OldPC is saved
PC, decode, 6. IDTR + interrupt
execute... Forever number is used to
Handler for 3. Interrupt occurs Handler for set PC to start of
Interrupt
Interrupt
Interrupt 6 Interrupt 6
Vectors
Vectors
(signal from interrupt handler
hardware) 7. Execution continues
Program
Program
(saves additional
Code
Code
Disk Disk state as first step)
Main Memory Main Memory
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6. CSC 369H1F, Fall 2012 Lecture 1
Bootstrapping Operating System Startup
• Hardware stores small program in non-volatile • Machine starts in system mode, so kernel code
memory can execute immediately
• BIOS – Basic Input Output System • OS initialization:
• Knows how to access simple hardware devices • Initialize internal data structures
• Disk, keyboard, display • Machine dependent operations are typically done
first
• When power is first supplied, this program starts • Create first process
executing • Switch mode to user and start running first process
• What does it do? • Wait for something to happen
• OS is entirely driven by external events
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Concurrency Next time…
• Every modern computer is a multiprocessor • Read about processes & threads (Chapter 2.1-2.2)
• CPU and device controllers can execute concurrently, competing
for memory cycles
• A memory controller synchronizes access to shared memory • Assignment 1 will be out sometime tomorrow
• Hardware Interrupts allow device controllers to signal the CPU (Tuesday, Sept. 11)
that some event has occurred (e.g. disk I/O complete, network • Refresh your memory of C, version control, and get
packet arrived, etc.)
started with threads and OS/161 early (before all your
• Generated by a hardware device
courses get busy)
• Software Interrupts are used to signal errors (e.g. division by zero)
or requests for OS service from a user program (a system call) • Should not take more than 6-8 hours to complete
• These types of interrupts are also called traps or exceptions • But start early so you can bring any questions to
tutorial on Thursday!
 An Operating System is an event-driven program
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