Chapter 3 OperatingSystem Structures

1
Chapter 3 Operating-System Structures
2
Outline

• System Components
• Operating System Services
• System Calls
• System Programs
• System Structure
• Virtual Machines
• System Design and Implementation
• System Generation
• Advanced Information

3
Common System Components

• Process Management
• Main Memory Management
• File Management
• I/O System Management
• Secondary-Storage Management
• Networking
• Protection System
• Command-Interpreter System

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Process Management

• A process is a program in execution
• Needs certain resources, including CPU time,
  memory, files, and I/O devices, to accomplish its
  task.
• Operating-system process vs. user process
• OS is responsible for
• Process creation and deletion
• Process suspension and resumption
• Provision of mechanisms for
• Process synchronization
• Process communication
• Deadlock handling
• Chapters 4-8

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Main-Memory Management

• Memory is a large array of words or bytes, each
  with its own address. It is a repository of
  quickly accessible data shared by the CPU and I/O
  devices
• Main memory is a volatile storage device. It
  loses its contents in the case of system failure
• A program must be mapped to absolute addresses
  and loaded into memory for execution
• OS is responsible for
• Keep track of which parts of memory are currently
  being used and by whom
• Decide which processes to load when memory space
  becomes available
• Allocate and de-allocate memory space as needed
• Chapters 9-10

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File Management

• File
• Uniform logical view of variable physical storage
  devices
• Collection of related information programs and
  data
• OS is responsible for
• File/Directory creation and deletion
• Support for manipulating files and directories
• Mapping files onto secondary storage
• File backup on stable (nonvolatile) storage media
• Chapters 11-12

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I/O System Management

• OS is responsible for hiding the peculiarities of
  specific hardware devices from the user by the
  I/O system
• The I/O system consists of
• A memory-management component that includes
  buffering, caching, and spooling
• A general device-driver interface
• Drivers for specific hardware devices
• Only the device driver knows the peculiarities of
  the specific device to which it is assigned
• Chapters 2, 13

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Secondary-Storage Management

• Secondary storage to back up main memory
• Main memory is too small and volatile
• Computer systems use disks as the principle
  on-line storage medium, for both programs and
  data
• Programs and data are brought into main memory
  when needed
• Secondary storage must be used for efficient
  because of the speed difference with CPU
• OS is responsible for
• Free space management
• Storage allocation
• Disk scheduling
• Chapter 14

9
Networking (Distributed Systems)

• A distributed system is a collection processors
  that do not share memory or a clock. Each
  processor has its own local memory.
• The processors in the system are connected
  through a communication network.
• Communication takes place using a protocol.
• A distributed system provides user access to
  various system resources.
• Access to a shared resource allows
• Computation speed-up
• Increased data availability
• Enhanced reliability
• Chapters 15-17

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Protection System

• Protection
• A mechanism for controlling access to both system
  and user resources by programs, processes, or
  users
• Ensure resources can be operated on by only those
  processes having gained proper authorization from
  OS
• The protection system must
• Distinguish between authorized and unauthorized
  usage
• Specify the controls to be imposed (Policy)
• Provide a means of enforcement (Mechanism)
• Chapter 18

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Command-Interpreter System

• Command interpreter
• Interface between users and OS
• Control-card interpreter, command-line
  interpreter, shell, mouse-based window-and-menu
  system
• Get the next statement and execute it
• Control statements
• Commands given to OS from command interpreter
• Deal with process creation and management, I/O
  handling, secondary-storage management,
  main-memory management, file-system access,
  protection, networking

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Operating System Services

• For the convenience of the programmer
• Program execution
• Load a program into memory and to run it
• End its execution, either normally or abnormally
• I/O operations file or I/O device
• since user programs cannot execute I/O operations
  directly, the operating system must provide some
  means to perform I/O.
• File-system manipulation
• Read, write, create, and delete files.

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Operating System Services (Cont.)

• For the convenience of the programmer (Cont.)
• Communications exchange of information between
  processes executing either on the same computer
  or on different systems tied together by a
  network
• Via shared memory or message passing
• Error detection ensure correct and consistent
  computing by detecting errors in the CPU and
  memory hardware, in I/O devices, or in user
  programs

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Additional Operating System Functions

• For ensuring efficient system operations
• Resource allocation allocating 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 ensuring that all access to system
  resources is controlled.
• Security ensuring that system resources are
  used and accessed as intended under all
  circumstances.

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System Calls
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Overview

• System calls provide the interface between a
  running program and the OS
• Switch from user mode to kernel mode
• Generally available as assembly-language
  instructions
• Languages defined to replace assembly language
  for systems programming allow system calls to be
  made directly (e.g., C, C, Win32 API)
• Categories
• Process control
• File manipulation
• Device manipulation
• Information maintenance
• Communication

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Overview (Cont.) -- Example

• Read data from one file and copy them to another
• Ask the names of the two files
• Prompt messages on the screen
• Read the file names from the keyboard
• Open the input file and create the output file
• A loop that reads from the input file and writes
  to the output file
• Close both files
• Terminate normally
• Error handling or abnormally terminate

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Overview (Cont.)

• Most of the details of the OS interface are
  hidden from the programmer by the compiler and by
  the run-time support package
• printf(.), cout()
• Compiled into a call to a run-time support
  routine that issues the necessary system calls,
  check for errors, and finally returned to the
  user program

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Parameter Passing to A System Call

• Parameter passing between a running program and
  the OS
• Pass parameters in registers.
• Store the parameters in a table in memory, and
  the table address is passed as a parameter in a
  register. (Linux)
• Push (store) the parameters onto the stack by the
  program, and pop off the stack by operating
  system.

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Passing of Parameters As A Table
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Types of System Calls

• Process control
• File management
• Device management
• Information maintenance
• Communications

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Process Control

• Halt execution either normally (end) or
  abnormally (abort)
• A process may load and execute another program
• Whether the existing one is lost, saved,
  concurrent executed?
• Create process or submit job concurrent executed
• Get process attribute, set process attribute
• Wait for a certain amount of time (wait time)
• Wait for a specific event to occur (wait event,
  signal event)
• Dump memory for debugging (dump)
• Time profile
• Allocate and free memory

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MS-DOS Execution
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UNIX Running Multiple Programs

• Shell fork and exec a program

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File, Device

• File Directory Management
• Create file, delete file
• Open, close
• Read, write, reposition
• Get file attribute
• Set file attribute

• Device Management
• Request device
• Release device
• Read, write, reposition
• Get device attribute
• Set device attribute
• Logically attach or detach devices (to a logical
  device file)
• The similarity between I/O devices and files is
  so great that many OS (including UNIX and DOS)
  merge the two into a combined file-device
  structure

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Information and Communication

• Information maintenance
• Get (set) time or date
• Get (set) system data
• of current users
• Version number
• Amount of free memory
• Get process, file, or device attribute
• Set process, file, or device attribute

• Communications
• Create, delete communication connection
• Send, receive messages
• Transfer status information
• Attach or detach remote devices (socket)

Communication Model 1. Message Passing 2. Shared
Message
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Communication Models
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System Programs

• System program provide a convenient environment
  for program development and execution
• Some are user interfaces to system calls
• Categories
• File management create/delete/rename/list files
  and directories
• Status information ask for date, time,
  available memory
• File modification editor
• Programming language support compiler,
  assembler, interpreter
• Program loading and execution loader and
  debugger
• Communications Email, talk, web browsing
• System utilities or application programs solve
  common problems

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System Programs (Cont.)

• Most users view of the operation system is
  defined by system programs, not the actual system
  calls.
• Command interpreter (CI) perhaps the most
  important system program for an OS
• How to implement the commands that a CI knows?
• Internal commands CI contains the command codes
• System programs
• Parameter passing
• Parameters interpretation is left up to the
  system program
• Slower

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System Structure

• Partition the task into small components
• Well-defined inputs, outputs, and function
• How to interconnect these components

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Simple Structure -- MS-DOS

• MS-DOS written to provide the most
  functionality in the least space
• Do not have a well-defined structure
• Not divided into modules
• Lack hardware protection and dual mode support
• Although MS-DOS has some structure, its
  interfaces and levels of functionality are not
  well separated

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Simple Structure Original UNIX

• Limited by hardware functionality, the original
  UNIX OS had limited structuring
• The UNIX OS consists of two separable parts
• Systems programs
• Kernel
• Consists of everything below the system-call
  interface and above the physical hardware
• Provides the file system, CPU scheduling, memory
  management, and other operating-system functions
• A large number of functions in one level

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General/Traditional UNIX Architecture
UI
API
SVR3, 4.3BSD, and earlier versions
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Layered Approach

• OS is divided into a number of layers (levels),
  each built on top of lower layers
• The bottom layer (layer 0), is the hardware
• The highest (layer N) is the user interface
• With modularity, each layer uses functions and
  services of only lower-level layers
• How to do vs. What to do
• Simplify debugging and system verification
• Clear interface
• Hide data structure,operation, hardware

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An Operating System Layer
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Layered Approach (Cont.)

• Shortcomings
• How to appropriately define the various layers
• Less efficient than other types
• Improvement
• Fewer layers with more functionality
• Provide most of the advantages of modularization
• Avoid the difficult problems of layer definition
  and interaction
• NT 4.0 moves layers from user space to kernel
  space and more closely integrating them

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OS/2 Layer Structure
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Micro-Kernels

• Moves as much from the kernel into user space.
• Smaller kernel
• Minimal process and memory management,
  communication facility
• Communication takes place between user modules
  using message passing
• Benefits
• Easier to extend a micro-kernel
• Easier to port the operating system to new
  architectures
• More reliable (less code is running in kernel
  mode)
• More secure

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Micro-Kernels (Cont.)

• Many services traditionally included in the
  operating system are now external subsystems
• Device drivers
• File systems
• Virtual memory manager
• Windowing system
• Security services
• Example
• Tru64 Unix (formally Digital UNIX)
• Apple MacOS X Server
• QNX real-time OS
• Windows NT (Hybrid) -- Win32, OS/2, POSIX

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Windows NT Client-Server Structure
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Virtual Machines

• A virtual machine takes the layered approach to
  its logical conclusion. It treats hardware and
  the operating system kernel as though they were
  all hardware
• A virtual machine provides an interface identical
  to the underlying bare hardware
• Each process is provided with a (virtual) copy of
  the underlying computer
• OS creates the illusion of multiple processes,
  each executing on its own processor with its own
  (virtual) memory.

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System Models
43
Virtual Machines (Cont.)

• The resources of the physical computer are shared
  to create the virtual machines
• CPU scheduling can create the appearance that
  users have their own processor
• Spooling and a file system can provide virtual
  card readers and virtual line printers
• A normal user time-sharing terminal serves as the
  virtual machine operators console

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Conceptual Implementation of VM

• How to run a MS-DOS program on Sun or DEC system?
• Create a virtual Intel machine on top of the
  native processor
• Intel instruction are translated by the Intel VM
  to the native instruction set

Intel Application
Intel VM
VM Interpretation
Sun Kernel
Sun hardware
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Java Technology

• Programming-language specification
• Object-oriented, architecture-neutral,
  distributed, secure, and multi-threaded
  programming language
• Application-Programming Interface (API)
• Base API graphics, I/O, utilities, networking
• Standard extension API enterprise, security,
  media
• Java Virtual Machine (JVM)
• A specification for an abstract computer
• Class loader load .class file and API
• Class verifier
• Run-time interpreter translate
  architecture-neutral bytecode into native machine
  language for the host computer
• Just-In-Time (JIT) compilers increase performance

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The Java Virtual Machine
JVM
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Advantages/Disadvantages of Virtual Machines

• The virtual-machine concept provides complete
  protection of system resources since each virtual
  machine is isolated from all other virtual
  machines. This isolation, however, permits no
  direct sharing of resources.
• A virtual-machine system is 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.
• The virtual machine concept is difficult to
  implement due to the effort required to provide
  an exact duplicate to the underlying machine.

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System Design and Implementation
49
System Design Goals

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

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Mechanisms and Policies

• Mechanisms determine how to do something,
  policies decide what will be done
• Timer construct is a mechanism for ensuring CPU
  protection, but deciding how long the timer is
  set for a particular user is a policy decision
• The separation of policy from mechanism is a very
  important principle, it allows maximum
  flexibility if policy decisions are to be changed
  later.

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System Implementation

• Traditionally written in assembly language, OS
  can now be written in higher-level languages
• Code written in a high-level language
• Can be written faster
• Is more compact
• Is easier to understand and debug
• Is easier to port (move to some other hardware)

52
System Generation (SYSGEN)

• OS are designed to run on any of a class of
  machines various sites, various peripheral
  configurations
• The system must be configured for each specific
  computer site
• System generation (SYSGEN)
• SYSGEN program obtains information concerning the
  specific configuration of the hardware system
• CPU (kind and number)
• Memory size, available devices
• OS options, parameter values (buffer size, max
  of processes)

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System Generation (Cont.)

• How to generate a system?
• Recompile
• Cause the creation of tables and selection of
  modules from a precompiled library
• Link modules together to form the generated OS
• SYSGEN is faster, but the generated OS may be
  overly general
• Completed table driven
• All the code is always part of the system, and
  selection occurs at execution time
• Most modern OS are constructed in this manner
• Size and generality of the generated system and
  the ease of modification as the hardware
  configuration changes

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Booting

• For a computer to start running
• Booting starting a computer by loading the
  kernel
• Bootstrap program the initial program
• Code stored in ROM that is able to locate the
  kernel, load it into memory, and start its
  execution
• Initialize all aspects of the system CPU
  registers, device controllers, memory contents
• Two step process a simple bootstrap loader
  fetches a more complex boot program from disk,
  which in turn loads the kernel
• PC, Sun Solaris
• Section 14.3.2 and Appendix A