COSC 4P13

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COSC 4P13

• Operating Systems Design and Implementation

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Course Description(1)

• The Goals for this course
• Understand UNIX
• Understand Operating Systems
• Prerequisites
• COSC 2P13 Introduction to Operating Systems
• COSC 2P91 Procedural Programming
• COSC 1P12 Computer Organization and Assembly
  Language

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Course Description(2)

• An intensive study of computer operating system
  design
• Multiprogramming
• Time-sharing
• Real-time processing
• Job and task control
• Synchronization of concurrent processes and
  processors
• Resource scheduling
• Protection
• Management of hierarchical storage.

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How to study this course

• Read and remember
• Read the book, remember the concepts and commands
• Think
• Think operating systems as natural administrative
  agents
• Practice
• Coding with UNIX, use and understand of UNIX
  commands and get the results

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The Textbook Used

• Uresh Vahalia, UNIX Internals The New Frontiers,
  Prentice Hall, 1996
• Why we use this book?
• UNIX is one of the popular operating systems of
  the world.
• If you understand UNIX, you can understand other
  operating systems.

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References

• William Stallings, Operating Systems,4th Ed.,
  Prentice Hall,2000
• A. Tanenbaum, Modern Operating Systems, 2nd ed.
  Prentice Hall 2001
• Kay A. Robbins and Steven Robbins, Practical UNIX
  Programming, Prentice Hall,1996
• W. R. Stevens, Advanced Programming in the UNIX
  Environment, Addison Wesley, 1992

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Operating System Overview

• Computer System
• Computer Hardware
• Components
• Registers
• Instruction execution
• Interrupt
• Memory Hierarchy and I/O
• Operating System
• Services of OS
• Major Achievements
• Characteristics of Modern OS

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Computer System
Application Programs
Utilities
Operating-System
Computer Hardware
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Computer Hardware

• Processor
• Main Memory
• referred to as real memory or primary memory
• volatile
• I/O modules
• secondary memory devices
• communications equipment
• terminals
• System interconnection
• communication among processors, memory, and I/O
  modules

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Computer Componentstop-level view
Memory

• MAR - Memory Address Register
• address for next read or write
• MBR - Memory Buffer Register
• data to be written into memory
• receives data read from memory
• I/OAR - I/O Address
• specifies a particular I/O device
• I/OBR - I/O Buffer
• exchange of data between an I/O module and the
  processor

.
.
.
CPU
Instruction
MAR
PC
Instruction
Instruction
.
IR
MBR
.
I/O AR
Data
I/O BR
Data
Data
I/O Module
Data
.
.
.
.
.
Buffers
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I/O Module Structure

• Data to/from system bus are buffered in data
  register(s)
• Status/Control register(s)
• I/O logic interact with CPU via control bus
• Contains logic specific to the interface of each
  device

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Processor Registers

• User-visible registers
• Data Registers
• Address Registers
• index register
• segment pointer
• stack pointer
• Condition Codes or Flags
• Control and Status Registers
• Program Counter (PC)
• Instruction Register (IR)
• Program Status Word (PSW)

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Instruction Execution

• Processor executes instructions in a program
• Instructions are fetched from memory one at a time

Fetch Cycle
Execute Cycle
Fetch Next Instruction
Execute Instruction
START
HALT
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Instruction Fetch and Execute

• The processor fetches the instruction from memory
• Program counter (PC) holds address of the
  instruction to be fetched next
• Program counter is incremented after each fetch

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Instruction Register

• Fetched instruction is placed here
• Types of instructions
• Processor-memory
• transfer data between processor and memory
• Processor-I/O
• data transferred to or from a peripheral device
• Data processing
• arithmetic or logic operation on data
• Control
• alter sequence of execution

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Interrupts

• An interruption of the normal processing of
  processor
• Improves processing efficiency
• Allows the processor to execute other
  instructions while an I/O operation is in
  progress
• A suspension of a process caused by an event
  external to that process and performed in such a
  way that the process can be resumed

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Classes of Interrupts

• Program
• arithmetic overflow
• division by zero
• execute illegal instruction
• reference outside users memory space
• Timer
• I/O
• Hardware failure

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Instruction Cycle with Interrupts
Fetch Cycle
Execute Cycle
Interrupt Cycle
Interrupts Disabled
Execute Instruction
Fetch Next Instruction
Check for Interrupt Process Interrupt
START
Interrupts Enabled
HALT
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Interrupt Handler

• A program that determines nature of the interrupt
  and performs whatever actions are needed
• Control is transferred to this program
• Generally part of the operating system

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Interrupt Cycle

• Processor checks for interrupts
• If no interrupts fetch the next instruction for
  the current program
• If an interrupt is pending, suspend execution of
  the current program, and execute the interrupt
  handler

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Simple Interrupt Processing
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Interrupts improve CPU usage

• I/O pgm prepares the I/O module and issues the
  I/O command (eg to printer)
• I/O pgm branches to user pgm
• User code gets executed during I/O operation (eg
  printing) no waiting
• User pgm gets interrupted (x) when I/O operation
  is done and branches to interrupt handler to
  examine status of I/O module
• Execution of user code resumes

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Multiple interrupts sequential order

• Disable interrupts during an interrupt
• Interrupts remain pending until the processor
  enables interrupts
• After interrupt handler routine completes, the
  processor checks for additional interrupts

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Multiple Interrupts priorities

• Higher priority interrupts cause lower-priority
  interrupts to wait
• Causes a lower-priority interrupt handler to be
  interrupted
• Example when input arrives from communication
  line, it needs to be absorbed quickly to make
  room for more input

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Cache/Main-Memory Structure
Memory Address
Slot Number
Tag
Block
0
0
1
1
2
Block (k words)
2
3
C - 1
Block Length (k words)
(b) Cache
Block
2n - 1
Word Length
(a) Main Memory
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Cache Design

• Cache size
• Block size
• Mapping function
• Replacement algorithm

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I/O Techniques

• Programmed I/O
• Interrupt-Driven I/O
• Direct Memory Access

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Programmed I/O
Insert Read command to I/O Module

• I/O module performs the action, not the processor
• Sets appropriate bits in the I/O status register
• No interrupts occur
• Processor is kept busy checking status

CPU I/O
Read Status of I/O Module
I/O CPU
Not Ready
Error Condition
Check Status
Ready
Read word from I/O Module
I/O CPU
Write word into memory
CPU Memory
No
Done?
Yes
Next Instruction
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Interrupt-Driven I/O
Insert Read command to I/O Module

• Processor is interrupted when I/O module ready to
  exchange data
• Processor is free to do other work
• No needless waiting
• Consumes a lot of processor time because every
  word read or written passes through the processor

CPU I/O
Do something else
Read Status of I/O Module
Interrupt
I/O CPU
Error Condition
Check Status
Ready
Read word from I/O Module
I/O CPU
Write word into memory
CPU Memory
No
Done?
Yes
Next Instruction
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Direct Memory Access
Issue Read block command to I/O module

• Transfers a block of data directly to or from
  memory
• An interrupt is sent when the task is complete
• The processor is only involved at the beginning
  and end of the transfer

CPU DMA
Do something else
Read status of DMA module
Interrupt
DMA CPU
Next Instruction
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Operating System

• Making computing power available to users by
  controlling the hardware
• a program that controls execution of application
  programs
• an interface between the user and hardware
• Directs the processor in the use of system
  resources
• Directs the processor when executing other
  programs

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Services Provided by the OS

• Facilities for Program creation
• editors, compilers, linkers, and debuggers
• Program execution
• loading in memory, I/O and file initialization
• Access to I/O and files
• deals with the specifics of I/O and file formats
• System access
• Protection of access to resources and data
• Resolves conflicts for resource contention

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Services Provided by the OS

• Error Detection
• internal and external hardware errors
• memory error
• device failure
• software errors
• arithmetic overflow
• access forbidden memory locations
• Inability of OS to grant request of application

• Error Response
• simply report error to the application
• Retry the operation
• Abort the application

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Services Provided by the OS

• Accounting
• collect statistics on resource usage
• monitor performance (eg response time)
• used for system parameter tuning to improve
  performance
• useful for anticipating future enhancements
• used for billing users (on multiuser systems)

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Operating System as a Resource Manager
Computer System
Memory
I/O Controller
Operating System Software
I/O Controller
.
.
Programs and Data
.
I/O Controller
.
.
.
Processor
Processor
OS
Programs
Data
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Ability to Evolve

• Must be able to adapt to hardware upgrades and
  new types of hardware. Examples
• Character vs graphic terminals
• Introduction of paging hardware
• Must be able to offer new services, eg internet
  support

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Major Achievements

• Processes
• Memory Management
• Information protection and security
• Scheduling and resource management
• System structure

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Memory Management

• Process isolation
• Automatic allocation and management
• Support for modular programming
• Protection and access control
• Long-term storage

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Virtual Memory

• Allows programmers to address memory from a
  logical point of view
• While program is running portions of the program
  and data are kept in blocks on disk

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File System

• Implements long-term store
• Information stored in named objects called files

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Categories of Security and Protection

• Access control
• regulate user access to the system
• Information flow control
• regulate flow of data within the system and its
  delivery to users
• Certification
• proving that access and flow control perform
  according to specifications

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Scheduling and Resource Management

• Fairness
• give equal and fair access to all processes
• Differential responsiveness
• discriminate between different classes of jobs
• Efficiency
• maximize throughput, minimize response time, and
  accommodate as many uses as possible

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Characteristics of Modern Operating Systems

• Microkernel architecture
• assigns only a few essential functions to the
  kernel
• address space
• interprocess communication (IPC)
• basic scheduling

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Characteristics of Modern Operating Systems

• Multithreading
• process
• is divided into threads that can run
  simultaneously
• Process is a collection of one or more threads
• Thread
• dispatchable unit of work
• executes sequentially and is interruptable

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Characteristics of Modern Operating Systems

• Symmetric multiprocessing
• there are multiple processors
• these processors share the same main memory and
  I/O facilities
• All processors can perform the same functions

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Characteristics of Modern Operating Systems

• Distributed operating systems
• provides the illusion of a single main memory
• used for distributed file system

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Characteristics of Modern Operating Systems

• Object-oriented design
• used for adding modular extensions to a small
  kernel
• enables programmers to customize an operating
  system without disrupting system integrity