Operating System Principles

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Operating SystemPrinciples

• Ku-Yaw Chang
• canseco_at_mail.dyu.edu.tw
• Assistant Professor, Department of Computer
  Science and Information Engineering
• Da-Yeh University

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Chapter 2 System Structures

• An operating system can be viewed from different
  vantage points
• Services that the system provides
• Programmers
• Interface available to users and programmers
• Users
• Components and their connections
• Operating system designer

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Chapter 2 Computer System Structures

1. Operating-System Services
2. User Operating-System Interface
3. System Calls
4. Types of System Calls
5. System Programs
6. Operating-System Design and Implementation

1. Operating-System Structure
2. Virtual Machines
3. Operating-System Generation
4. System Boot
5. Summary
6. Exercises

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2.1 Operating-System Services

• Common services (1/2)
• User interfaces
• Command-line interface (CLI)
• Batch interface
• Graphical user interface (GUI)
• Program execution
• to load a program into memory and to run it.
• I/O operations
• user programs cannot execute I/O operations
  directly

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2.1 Operating-System Services

• Common services (1/2)
• File-system manipulation
• capability to read, write, create, and delete
  files
• Communications
• exchange of information between processes
• Implemented via shared memory or message passing
• Error detection
• ensure correct computing by detecting errors in
  the CPU and memory hardware, in I/O devices, or
  in user programs

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Additional Functions

• Not for helping the user, but rather for ensuring
  efficient system operations
• Resource allocation
• allocate resources to multiple users or multiple
  jobs running at the same time
• Accounting
• keep track of and record which users use how much
  and what kinds of computer resources for account
  billing or for accumulating usage statistics
• Protection and security
• ensure that all access to system resources is
  controlled
• each user authenticate himself or herself to the
  system

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Chapter 2 Computer System Structures

1. Operating-System Services
2. User Operating-System Interface
3. System Calls
4. Types of System Calls
5. System Programs
6. Operating-System Design and Implementation

1. Operating-System Structure
2. Virtual Machines
3. Operating-System Generation
4. System Boot
5. Summary
6. Exercises

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User Operating-System Interface

• Two approaches for users to interact with OS
• Command-line interface (CLI) or command
  interpreter
• Graphical user interface (GUI)

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2.2.1 Command Interpreter

• Command interpreter
• Included in the OS kernel
• Treated as a special program
• Windows XP and UNIX
• Also known as shells
• Multiple command interpreters to choose from
• On UNIX and Linux systems
• Bourne shell
• C shell
• See what was my login shell?
• saturn echo SHELL
• /bin/csh

• Bourne-Again shell
• Korn shell

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2.2.1 Command Interpreter

• Main function
• To get and execute the next user-specified
  command
• Example file manipulation
• create, delete, list, print, copy, execute
• Internal vs. external command
• Internal
• The command interpreter contains the code to
  execute the command
• External
• Use the command to identify a file to be loaded
  into memory and executed

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2.2.2 Graphical User Interfaces

• User-friendly desktop metaphor interface
• A mouse-based window-and-menu system
• Usually mouse, keyboard, and monitor
• Icons represent files, programs, actions, etc
• Various mouse buttons over objects in the
  interface cause various actions (provide
  information, options, execute function, open
  directory (known as a folder)
• Invented at Xerox PARC

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2.2.2 Graphical User Interfaces

• Many systems now include both CLI and GUI
  interfaces
• Microsoft Windows is GUI with CLI command shell
• command.com or cmd.exe
• Apple Mac OS X as Aqua GUI interface with UNIX
  kernel underneath and shells available
• Solaris is CLI with optional GUI interfaces (Java
  Desktop, KDE)

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Chapter 2 Computer System Structures

1. Operating-System Services
2. User Operating-System Interface
3. System Calls
4. Types of System Calls
5. System Programs
6. Operating-System Design and Implementation

1. Operating-System Structure
2. Virtual Machines
3. Operating-System Generation
4. System Boot
5. Summary
6. Exercises

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2.3 System Calls

• The interface between a process and the OS
• Assembly-language
• Higher-level language
• C, C and Perl
• Mostly accessed by programs via a high-level
  Application Program Interface (API) rather than
  direct system call use
• Win32 API for Windows
• POSIX API for POSIX-based systems (including
  virtually all versions of UNIX, Linux, and Mac OS
  X)
• Java API for the Java virtual machine (JVM)

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2.3 System Calls

• Why use APIs rather than system calls?
• Better program portability
• Easy to work with

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Depiction of XP Architecture
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Different Types of I/O

• Low-level I/O (system call)
• _open, _close
• _read, _write
• Stream I/O
• fopen, fclose
• fread, fwrite
• WIN32 API
• CreateFile, CloseHandle
• ReadFile, WriteFile

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Example of Standard API

• Consider the ReadFile() function in the Win32 API
• a function for reading from a file
• A description of the parameters passed to
  ReadFile()
• HANDLE filethe file to be read
• LPVOID buffera buffer where the data will be
  read into and written from
• DWORD bytesToReadthe number of bytes to be read
  into the buffer
• LPDWORD bytesReadthe number of bytes read during
  the last read
• LPOVERLAPPED ovlindicates if overlapped I/O is
  being used

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2.3 System Calls

• Even simple programs may make heavy use of the
  operating system.
• To read data from one file and to copy them to
  another file
• Requiring a sequence of system calls
• Details are hidden from the programmer

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System Call Sequence
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System Call Implementation

• Typically, a number associated with each system
  call
• System-call interface maintains a table indexed
  according to these numbers
• The system call interface invokes intended system
  call in OS kernel and returns status of the
  system call and any return values
• The caller need know nothing about how the system
  call is implemented
• Just needs to obey API and understand what OS
  will do as a result call
• Most details of OS interface hidden from
  programmer by API
• Managed by run-time support library (set of
  functions built into libraries included with
  compiler)

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The Handling of open() System Call
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Standard C Library Example

• C program invoking printf() library call, which
  calls write() system call

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System Call Parameter Passing

• Three general methods used to pass parameters to
  the OS
• Simplest pass the parameters in registers
• In some cases, may be more parameters than
  registers
• Parameters stored in a block, or table, in
  memory, and address of block passed as a
  parameter in a register
• This approach taken by Linux and Solaris
• Parameters placed, or pushed, onto the stack by
  the program and popped off the stack by the
  operating system
• Block and stack methods do not limit the number
  or length of parameters being passed

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Parameter Passing via Table
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Chapter 2 Computer System Structures

1. Operating-System Services
2. User Operating-System Interface
3. System Calls
4. Types of System Calls
5. System Programs
6. Operating-System Design and Implementation

1. Operating-System Structure
2. Virtual Machines
3. Operating-System Generation
4. System Boot
5. Summary
6. Exercises

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2.4 Types of System Calls

• Five major categories
• Process control
• File management
• Device management
• Information maintenance
• Communications

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2.4.1 Process Control

• A running program
• Halt its execution
• normally (end)
• abnormally (abort)
• A dump of memory
• Load and execute another program
• fork()
• exec()

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MS-DOS
At System Start-up
Running a Program
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FreeBSD running multiple programs
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2.4.5 Communication

• Two common models
• Message-passing
• Messages can be exchanged either directly or
  indirectly through a common mailbox
• A connection must be established
• open, connection, close
• Useful for smaller amounts of data
• Easier for intercomputer communication
• Shared-memory
• Create and gain access to regions of memory owned
  by other processes
• Maximum speed and convenience

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2.4.5 Communication
Message Passing
Shared Memory
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Chapter 2 Computer System Structures

1. Operating-System Services
2. User Operating-System Interface
3. System Calls
4. Types of System Calls
5. System Programs
6. Operating-System Design and Implementation

1. Operating-System Structure
2. Virtual Machines
3. Operating-System Generation
4. System Boot
5. Summary
6. Exercises

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2.5 System Programs

• System programs provide a convenient environment
  for program development and execution
• File management
• Status information
• File modification
• Programming language support
• Program loading and execution
• Communication
• System utilities or application programs
• To solve common problems, or perform common
  operations
• Web browsers and word processors
• Games

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2.5 System Programs

• Command interpreter
• The most important system program
• Two approaches
• The command interpreter contains the code to
  execute the command.
• Internal command
• Implement most commands by system programs
• External command

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Chapter 2 Computer System Structures

1. Operating-System Services
2. User Operating-System Interface
3. System Calls
4. Types of System Calls
5. System Programs
6. Operating-System Design and Implementation

1. Operating-System Structure
2. Virtual Machines
3. Operating-System Generation
4. System Boot
5. Summary
6. Exercises

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2.6.1 Design Goals

• User goals
• should be convenient to use, easy to learn,
  reliable, safe, and fast
• System goals
• should be easy to design, implement, and
  maintain, as well as flexible, reliable,
  error-free, and efficient

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2.6.2 Mechanisms and Policies

• General software engineering principles are
  applicable to operating systems
• Separation of policy from mechanism
• For flexibility
• Mechanisms
• How to do something
• A general mechanism
• Policies
• What will be done
• Change across places or over time

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2.6.2 Mechanisms and Policies

• Microkernel-based
• Take the separation of mechanism and policy to
  one extreme
• Windows / Apple Macintosh (Mac OS X)
• Both mechanism and policy are encoded in the
  system

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2.6.3 Implementation

• Traditionally written in assembly language,
  operating systems can now be written in
  higher-level languages such as C/C
• Linux and Windows XP are written mostly in C
• Code written in a high-level language
• can be written faster
• more compact
• easier to understand and debug
• easier to port (move to some other hardware)
• Disadvantage
• Reduced speed and increased storage requirements

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Chapter 2 Computer System Structures

1. Operating-System Services
2. User Operating-System Interface
3. System Calls
4. Types of System Calls
5. System Programs
6. Operating-System Design and Implementation

1. Operating-System Structure
2. Virtual Machines
3. Operating-System Generation
4. System Boot
5. Summary
6. Exercises

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2.7 Operating-System Structure

• To partition the task (OS) into small components
  (modules)
• Not one monolithic system
• Available approaches
• Simple structure
• Layered approach
• Microkernels
• Modules

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2.7.1 Simple Structure

• MS-DOS
• written to provide the most functionality in the
  least space
• not divided into modules
• Although having some structure, its interfaces
  and levels of functionality are not well separated

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MS-DOS Layer Structure
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2.7.1 Simple Structure

• UNIX (original)
• consists of two separable parts
• Kernel
• everything below the system-call interface and
  above the physical hardware
• System programs

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Unix System Structure
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2.7.2 Layered Approach

• OS is broken into a number of layers (or levels)
• Each built on top of lower layers
• The bottom layer (layer 0) is the hardware
• The highest layer (layer N) is the user interface
• With modularity, layers are selected such that
  each uses functions (operations) and services of
  only lower-level layers.
• Simplify debugging and system verification
• Difficult to define each layer
• Less efficient overhead

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A Layered OS
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An OS layer
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OS/2 layer structure
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Windows NT

• First release
• A highly layer-oriented organization
• Low performance (compared to Windows 95)
• NT 4.0
• Move layers from user space to kernel space
• Closely integration

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2.7.3 Microkernels

• Mach
• Developed at Carnegie Mellon University in the
  mid-1980s
• Use the microkernel approach
• Removing non-essential components from the kernel
• Implement them as system- and user-level programs
• A smaller kernel
• Main function
• To provide a communication facility

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2.7.3 Microkernels

• Benefits
• easier to extend
• easier to port
• more security
• more reliability
• Examples
• Tru64 UNIX UNIX Mach kernel
• MacOS X based on Mach kernel
• QNX a real-time OS
• Windows NT ( a hybrid structure)

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Windows NT client-server structure
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2.7.4 Modules

• Most modern operating systems implement kernel
  modules
• Uses object-oriented approach
• Each core component is separate
• Each talks to the others over known interfaces
• Each is loadable as needed within the kernel
• Overall, similar to layers but with more flexible

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Solaris Loadable Modules
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Chapter 2 Computer System Structures

1. Operating-System Services
2. User Operating-System Interface
3. System Calls
4. Types of System Calls
5. System Programs
6. Operating-System Design and Implementation

1. Operating-System Structure
2. Virtual Machines
3. Operating-System Generation
4. System Boot
5. Summary
6. Exercises

58
2.8 Virtual Machines

• A computer system is made up of layers
• Hardware is the lowest
• Virtual machines
• take the layered approach to its logical
  conclusion
• treat hardware and the operating system kernel as
  though they were all hardware
• provide an interface identical to the underlying
  bare hardware
• OS creates the illusion of multiple processes
• each has on its own processor with its own
  (virtual) memory

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System Models
Non-virtual Machine
Virtual Machine
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2.8.1 Implementation

• Difficult to implement
• To provide an exact duplicate of the underlying
  machine
• User mode
• Monitor mode
• Time the major difference
• I/O
• Less time or more time
• CPU
• Multiprogrammed among many virtual machines

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2.8.2 Benefits

• Provide complete protection of system resources
• Each virtual machine is isolated from all other
  virtual machines.
• Permits no direct sharing of resources
• A perfect vehicle for operating-systems research
  and development
• System development is done on the virtual
  machine, instead of on a physical machine and so
  does not disrupt normal system operation
• Solve system compatibility problems

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2.8.3 Examples

• 2.8.3.1 VMware
• a popular commercial application
• abstract Intel 80X86 hardware
• run several guest operating systems concurrently

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VMware Architecture
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2.8.3.2 Java Virtual Machine

• A very popular object-oriented language
• By Sun Microsystems in late 1995
• Consists of
• A language specification
• A large API library
• A specification for a Java virtual machine (JVM)
• A class loader
• A class verifier
• A Java interpreter

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2.8.3.2 Java Virtual Machine

• A Java program consists of one or more classes.
• For each class, the Java compiler produce an
  architecture-neutral bytecode output (.class)
  file
• Run on any implementation of the JVM

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Java virtual machine
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2.8.3.2 Java Virtual Machine

• Garbage collection
• Reclaim memory from objects no longer in use and
  return it to the system
• Just-in-time (JIT) compiler
• The first time a Java method is invoked, the
  bytecodes are turned into native machine language
  for the host computer
• These operations are cached for later use

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Chapter 2 Computer System Structures

1. Operating-System Services
2. User Operating-System Interface
3. System Calls
4. Types of System Calls
5. System Programs
6. Operating-System Design and Implementation

1. Operating-System Structure
2. Virtual Machines
3. Operating-System Generation
4. System Boot
5. Summary
6. Exercises

69
2.9 Operating System Generation

• Operating systems are designed to run on any of a
  class of machines
• must be configured for each specific computer
  site.
• System generation (SYSGEN)
• obtain information concerning the specific
  configuration of the hardware system.
• from a given file
• ask the operator
• probe the hardware directly

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Chapter 2 Computer System Structures

1. Operating-System Services
2. User Operating-System Interface
3. System Calls
4. Types of System Calls
5. System Programs
6. Operating-System Design and Implementation

1. Operating-System Structure
2. Virtual Machines
3. Operating-System Generation
4. System Boot
5. Summary
6. Exercises

71
2.10 System Boot

• Booting
• starting a computer by loading the kernel
• Bootstrap program (bootstrap loader)
• code stored in ROM that is able to locate the
  kernel, load it into memory, and start its
  execution
• two-step process
• A simple bootstrap loader fetches a more complex
  boot program from disk

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Chapter 2 Computer System Structures

1. Operating-System Services
2. User Operating-System Interface
3. System Calls
4. Types of System Calls
5. System Programs
6. Operating-System Design and Implementation

1. Operating-System Structure
2. Virtual Machines
3. Operating-System Generation
4. System Boot
5. Summary
6. Exercises

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Summary

• P.68 P.69

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Chapter 2 Computer System Structures

1. Operating-System Services
2. User Operating-System Interface
3. System Calls
4. Types of System Calls
5. System Programs
6. Operating-System Design and Implementation

1. Operating-System Structure
2. Virtual Machines
3. Operating-System Generation
4. System Boot
5. Summary
6. Exercises

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Exercises

• 2.5
• 2.6
• 2.9
• 2.10

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The End