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Chapter 13
Operating Systems: An Overview
The Architecture of Computer Hardware
and Systems Software:
An Information Technology Approach
3rd Edition, Irv Englander
John Wiley and Sons 2003
Wilson Wong, Bentley College
Linda Senne, Bentley College
Bare Bones Computer System
 Does not load instructions into main
memory
 No user interface except for I/O routines
provided with executing program
 Is idle when waiting for user input
 No facility to store, retrieve, or
manipulate files
 No ability to control peripheral devices
 Can run only one program at a time
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Integrated Computer Environment
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Operating System – Basic Services
 Programs that accept commands and
requests from a user and a user’s
program
 Manages, loads, and executes
programs
 Manages hardware resources of the
computer
 Act as an interface between the user
and the system
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Operating System – Additional Services
 Provides interfaces for the user and the user’s
programs
 File support services
 I/O support services
 Means of starting the computer
 Bootstrapping or booting the computer
 Initial Program Load (IPL)
 Handles all interrupt processing
 Network services
 Provides tools and services for concurrent processing
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Additional Services Required by
Concurrent Processing
 Allocates resources such as memory,
CPU time, and I/O devices to programs
 Protects users and programs from each
other and provides for inter-program
communication
 Provides feedback to the system
administrators to permit performance
optimization of the computer system
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OS Parts
 Memory Resident
 Always loaded in memory
 Commonly called the kernel
 Contains essential services required by other parts of the
operating system and applications.
 Typically responsible for managing memory management,
processes and tasks, and secondary storage
 Memory Non-resident
 Applications
 Infrequently used programs, software tools, and commands
 Bootstrap program
 Diskless workstations or thin clients
 Programs, including the OS, are located on another
computer on the network
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Simplified Diagram of Operating
System Services
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OS Degree of Activity
 Interactive
 Also known as conversational systems
 Batch processing
 User submits programs or jobs for
processing
 Little to no user interaction
 Event driven
 Interrupts or service requests
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Hardware and the OS
 A hardware platform may support a variety of
operating systems
 An operating system may work on a variety of
platforms
 A standard operating system that works on different
hardware
 Provides program and file portability
 Enables user efficiency through recognizable interface
 Is implemented through a systems programming language
like C or C++ as opposed to assembly language
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Single Job Processing
 Only one program is loaded into
memory and executed
 Example: MS-DOS
 Memory resident components
 Command interface shell
 I/O routines, including BIOS
 File management system
 User program in control
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OS Regains Control
 When program is finished control is
transferred back to the command
interpreter
 If the user’s program requests I/O
 The user wishes to stop the program
execution via a keyboard interrupt
 System malfunctions
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Single Job Processing
Disadvantages
 Lack of security
 Programs can overwrite the resident OS
 Programs can write directly to I/O devices
 System provides minimum memory
management and no scheduling
 CPU is often idle awaiting the completion of
I/O operations
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Concurrent Operations
 Multitasking (multiprogramming) vs.
multiprocessing which implies multiple
CPUs
 Concurrent processing vs. simultaneous
processing
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Achieving Multitasking
 While one program is waiting for I/O to
take place, another program is using the
CPU to execute instructions.
 Time-slicing. The CPU may be
switched rapidly back and forth between
different programs
 Dispatching is the process of selecting
which program to run at any given
instant
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Sharing the CPU during I/O Breaks
 I/O represents a large percentage of a
typical program’s execution
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Time-sharing the CPU
Time slicing
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Services and Facilities

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Command processor
File management system
I/O control system
Process control management and interprocess
communication
Memory management
Scheduling system
Secondary storage management
System protection management
Network management, communication support, and
communication interfaces
System Administration
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User Interface and
Command Execution Services
 Types of user interfaces
 CLI - Command Line Interface
 GUI - Graphical User Interface
 Menu environment
 Shell
 User interface and command processor that interacts with
the kernel
 UNIX: C, Bourne and Korn shells
 Command Languages
 IBM Mainframes – JCL
 MS Windows – BAT files, Windows Scripting Host
 UNIX – shell scripts
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File Management
 File - logical unit of storage
 Basic file management system provides
 Directory structures for each I/O device
 Tools to copy and move files
 Information about each file in the system and the tools to
access that information
 Security mechanisms to protects files and control access
 Additional file management features
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Backup, emergency retrieval and recovery
File compression
Transparent network file access
auditing
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I/O Services and
Process Control Management
 I/O services
 Startup configuration
 Device drives that implement interrupts and provide
other techniques for handling I/O
 Plug and play: hot swapping, hot plugging
 Process control management
 A process is an executing program
 A thread is an individually executable part of a
process
 Interprocess messaging services

Example: a pipe in UNIX or DOS that is a temporary
software connection between two programs or commands
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Memory Management
 Keeps track of memory
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Identifies programs loaded into memory
Amount of space each program uses
Available remaining space
Prevents programs from reading and writing
memory outside of their allocated space
 Maintains queues of waiting programs
 Allocates memory to programs that are next
to be loaded
 Deallocates a program’s memory space upon
program completion
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Scheduling
 High-level scheduling
 Placed in queue based on level of priority and eventually
executed
 Dispatching
 Actual selection of processes that will be executed at any
given time
 Preemptive – uses clock interrupts
 Non-preemptive – program voluntarily gives up control
 Context switching
 Transfer control to the process that is being dispatched
 Nonpreemptive: program voluntarily gives up control
 Preemptive: uses clock interrupt for multitasking
 Processing requirements
 CPU vs. I/O bound
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Secondary Storage and Security
 Secondary storage management
 Optimizes completion of I/O tasks for efficient disk
usage
 Combination of hardware and software
 Security and protection services
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Protect OS from users
Protect users from other users
Prevent unauthorized entry to system
Prevent unauthorized system use by authorized
users
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Network and Communication Services
 TCP-IP protocol suite
 Locate and connect to other computers
 Access files, I/O devices, and programs from
remote systems
 Support distributed processing
 Network Applications
 Email, remote login, Web services, streaming
multimedia, voice over IP telephony, VPN
 Interface between communication software
and OS I/O control system that provides
network access
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System Administration Support
 System configuration
and setting group
configuration policies
 Adding and deleting
users
 Modifying user
privileges
 System security
 Files systems
management
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Operating Systems: An Overview
 Network administration
 Backups
 Software installations
and upgrades
 OS installations
(system generation),
patches, and upgrades
 System tuning and
optimization
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Monolithic Kernel
 Drawback: stability
and integrity
 Examples:
 UNIX
 Windows NT
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Hierarchical
 Requests pass
through
intermediate
layers
 Examples
 Multics
 Data General
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Microkernel
 Minimum essential functionality
 Client-server system on same system
 Clients request services from microkernel which
passes message onto appropriate server
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Mach OS Kernel
 Microkernel implementation
 Includes
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Message passing
Interrupt processing
Virtual memory management
Scheduling
Basic set of I/O drivers
 Macintosh OS X, IBM AIX on RS/6000
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Types of Operating Systems
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Single user, single tasking
Single user, multitasking
Multi-user, multitasking
Distributed systems
 Processing power distributed among computers in
a cluster or network
 Network servers
 Real-time systems
 Embedded systems
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Bootstrapping
 Execution begins with bootstrap loader
(mini-loader, IPL) stored in ROM
 Looks for OS program in a fixed location
 Loads OS into RAM
 Transfers control to starting location of
OS
 Loader program in OS used to load and
execute user programs
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Bootstrapping
 Cold vs.
warm boot
(does not
retest the
system)
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Copyright 2003 John Wiley & Sons
All rights reserved. Reproduction or translation of this
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Operating Systems: An Overview
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