The architecture of computer hardware and systems software an information technology approach ch13

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


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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