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Invitation to Computer Science
6th Edition
Chapter 6
An Introduction to System
Software and Virtual Machines
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
Allows only numeric memory addresses
Is difficult to change
Is difficult to create data
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Assemblers and Assembly Language
• Assembly languages
– Designed to overcome shortcomings of machine
languages
– Each symbolic assembly language instruction is
translated into exactly one binary machine language
instruction
– Create a more productive, user-oriented
environment
– Earlier termed second-generation languages
– Now viewed as low-level programming languages
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Assembly Language
• 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
– Use of symbolic operation codes rather than numeric
(binary) ones
– Use of symbolic memory addresses rather than
numeric (binary) ones
– Pseudo-operations that provide useful user-oriented
services such as data generation
• 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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Typical Instruction of Assembly
Language
• (Label): (op code mnemonic) (address field) (comments)
• Label: permanent identification for this instruction of data, like an
address of command.
• op code mnemonic: symbolic command name
• Address field: symbolic address of the data
• Comments: for reading
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How to declare data in assembly
language?
• Example: (pseudo-op)
FIVE:
.DATA
Address
53
content
0000000000000101
NEGSEVEN:
Address
54
.DATA
-7
content
1000000000000111
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How to use data?
• LOAD FIVE
• ADD NEGSEVEN
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Examples of Assembly Language
Code
• Arithmetic expression
A=B+C–7
(Assume that B and C have already been
assigned values)
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Examples of Assembly Language
Code
• Assembly language translation
LOAD
B
--Put the value B into register R.
ADD
C
--R now holds the sum (B + C).
SUBTRACT
SEVEN
--R now holds the expression (B + C - 7).
STORE
A
--Store the result into A.
:
--These data should be placed after the
HALT.
A:
.DATA
0
B:
.DATA
0
C:
.DATA
0
SEVEN:
.DATA
7
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--The constant 7.
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Examples of Assembly Language
Code
• Conditional operation
– Tests and compares value
• Algorithmic problem-solving cycle
– One of the central themes of computer science
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Examples of Assembly Language
Code
• Problem
– Read in a sequence of non-negative numbers, one
number at a time, and compute a running sum
– When you encounter a negative number, print out
the sum of the non-negative values and stop
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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
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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)
• Pass
– Process of examining and processing every
assembly language instruction in the program, one
instruction at a time
• Assemblers make two pass of the source code to
generate object program.
– First pass: Handle memory address and bind
physical address
– Second pass: Handle data generation and translate
source program into object program.
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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 Operating
Systems Development
• First-generation system software
– Roughly 1945–1955
– No operating systems and very little software
support
• Second-generation system software
– Called batch operating systems (1955–1965)
• 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 Operating
Systems Development (continued)
• Third-generation operating systems
– Multiprogrammed operating systems (1965–1985)
– 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 Operating
Systems 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 (1985–present)
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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 Operating
Systems 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
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