Invitation to Computer Science 5th Edition

1
Invitation to Computer Science 5th Edition

• Chapter 6
• An Introduction to System Software and
  Virtual Machines

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Objectives

• In this chapter, you will learn about
• System software
• Assemblers and assembly language
• Operating systems

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Introduction

• Naked machine
• Hardware bereft of any helpful user-oriented
  features
• Data as well as instructions must be represented
  in binary
• To make a Von Neumann computer usable
• Create an interface between the user and the
  hardware

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System Software

• The virtual machine
• System software collection of computer programs
  that manage the resources of a computer and
  facilitate access to those resources
• Software sequences of instructions that solve a
  problem

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Figure 6.1 The Role of System Software
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Types of System Software

• Operating system
• Communicates with users
• Determines what they want
• Activates other system programs, applications
  packages, or user programs to carry out their
  request

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Types of System Software (continued)

• User interface
• Provides user with an intuitive visual overview
• Language services (assemblers, compilers, and
  interpreters)
• Allow you to write programs in a high level
• Memory managers
• Allocate memory space for programs and data
• Information managers
• Handle the organization, storage, and retrieval
  of information on mass storage devices

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Figure 6.2 Types of System Software
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Types of System Software (continued)

• I/O systems
• Allow you to easily and efficiently use the input
  and output devices that exist on a computer
  system
• Scheduler
• Keeps a list of programs ready to run on the
  processor and selects the one that will execute
  next
• Utilities
• Library routines that provide useful services
  either to a user or to other system routines

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Assemblers and Assembly Language

• Problems with machine language
• Uses binary
• Is difficult to change
• Is difficult to create data

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Assembly Language

• Assembly language
• Low-level programming language
• Each symbolic assembly language instruction is
  translated into exactly one binary machine
  language instruction
• High-level programming languages
• User oriented
• Not machine specific
• Use both natural language and mathematical
  notation in their design

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Figure 6.3 The Continuum of Programming Languages
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Assembly Language(continued)

• Source program
• Program written in assembly language
• Object program
• Source program must be translated into a
  corresponding machine language program
• Assembler
• System software that carries out translation
• Advantage of assembly language
• Allows use of symbolic addresses

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Figure 6.4 The Translation/ Loading/Execution
Process
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Figure 6.5 Typical Assembly Language Instruction
Set
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Assembly Language(continued)

• Advantages of symbolic labels
• Program clarity
• Maintainability
• Pseudo-op
• Invokes the service of the assembler
• Provides program construction

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Figure 6.6 Structure of a Typical Assembly
Language Program
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Examples of Assembly Language Code

• Conditional operation
• Tests and compares values
• Algorithmic problem-solving cycle
• One of the central themes of computer science

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Figure 6.7 Algorithm to Compute the Sum of Numbers
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Figure 6.8 Assembly Language Program to Compute
the Sum of Nonnegative Numbers
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Translation and Loading

• Assembler
• Translates a symbolic assembly language program
  into machine language
• Tasks performed
• Convert symbolic op codes to binary
• Convert symbolic addresses to binary
• Perform the assembler services requested by the
  pseudo-ops
• Put the translated instructions into a file for
  future use

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Translation and Loading (continued)

• Op code table
• Alphabetized list of all legal assembly language
  op codes and their binary equivalents
• In assembly language
• A symbol is defined when it appears in the label
  field of an instruction or data pseudo-op
• Pass
• Process of examining and processing every
  assembly language instruction in the program, one
  instruction at a time

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Figure 6.9 Structure of the Op Code Table
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Figure 6.10 Generation of the Symbol Table
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Translation and Loading (continued)

• First pass over source code
• Assembler looks at every instruction
• Binding
• Process of associating a symbolic name with a
  physical memory address
• Primary purposes of the first pass of an
  assembler
• To bind all symbolic names to address values
• To enter those bindings into the symbol table

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Translation and Loading (continued)

• Location counter
• Variable used to determine the address of a given
  instruction
• Second pass
• Assembler translates source program into machine
  language
• After completion of pass 1 and pass 2
• Object file contains the translated machine
  language object program

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Figure 6.11 Outline of Pass 1 of the Assembler
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Figure 6.12 Outline of Pass 2 of the Assembler
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Figure 6.13 Example of an Object Program
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Operating Systems

• Operating system
• Waits for requests and activates other system
  programs to service these requests
• System commands
• Used to translate, load, and run programs

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Functions of an Operating System

• The user interface
• Operating system commands usually request access
  to hardware resources, software services, or
  information
• To communicate with a user, a GUI supports visual
  aids and point-and-click operations

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Figure 6.14 Some Typical Operating System
Commands
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Figure 6.15 User Interface Responsibility of the
Operating System
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Figure 6.16 Example of a Graphical User Interface
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System Security and Protection

• Operating system
• Controls access to the computer and its resources
• Safeguards password file
• Sometimes uses encryption to provide security
• Access control
• Use of a legal user name and password

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Figure 6.17 Authorization List for the File GRADES
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Efficient Allocation of Resources

• I/O controller
• Frees the processor to do useful work while the
  I/O operation is being completed
• To ensure that a processor does not sit idle if
  there is useful work to do
• Operating system keeps a queue of programs that
  are ready to run

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The Safe Use of Resources

• Operating system
• Prevents programs or users from attempting
  operations that cause the computer system to
  enter a frozen state
• Deadlock
• Each program is waiting for a resource to become
  available that will never become free

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The Safe Use of Resources (continued)

• Deadlock prevention
• Operating system uses resource allocation
  algorithms that prevent deadlock from occurring
  in the first place
• Deadlock recovery algorithms
• Detect and recover from deadlocks

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Summary of OS Responsibilities

• Major responsibilities of operating systems
• User interface management (a receptionist)
• Control of access to system and files (a security
  guard)
• Program scheduling and activation (a dispatcher)
• Efficient resource allocation (an efficiency
  expert)
• Deadlock detection and error detection (a traffic
  officer)

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Historical Overview of OperatingSystems
Development

• First-generation system software
• Roughly 19451955
• No operating systems and very little software
  support
• Second-generation system software
• Called batch operating systems (19551965)
• Command language
• Commands specifying to the operating system what
  operations to perform on programs

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Figure 6.18 Operation of a Batch Computer System
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Figure 6.19 Structure of a Typical Batch Job
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Historical Overview of OperatingSystems
Development (continued)

• Third-generation operating systems
• Multiprogrammed operating systems (19651985)
• Many user programs are simultaneously loaded into
  memory
• User operation codes could be included in any
  user program
• Privileged operation codes use restricted to the
  operating system or other system software

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Historical Overview of OperatingSystems
Development (continued)

• Time-sharing system
• Many programs can be stored in memory
• Allows programmer to enter system commands,
  programs, and data online
• Distributed environment
• Much of the computing was done remotely in the
  office, laboratory, classroom, and factory
• Network operating system
• Fourth-generation operating system (1985present)

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Figure 6.20 Configuration of a Time-Shared
Computing System
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Figure 6.21 A Local Area Network
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Historical Overview of OperatingSystems
Development (continued)

• Real-time operating system
• Manages resources of embedded computers that are
  controlling ongoing physical processes
• Guarantees that it can service important requests
  within a fixed amount of time

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The Future

• Multimedia user interfaces
• Will interact with users and solicit requests in
  a variety of ways
• Parallel processing operating system
• Can efficiently manage computer systems
  containing tens, hundreds, or even thousands of
  processors
• Distributed computing environment
• Users do not need to know the location of a given
  resource within the network

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Figure 6.23 Structure of a Distributed System
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Figure 6.24 Some of the Major Advances in
Operating Systems Development
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Summary

• System software
• Acts as an intermediary between the users and the
  hardware
• Assembly language
• Creates a more productive, user-oriented
  environment than machine language
• An assembler
• Translates an assembly language program into a
  machine language program