1. Invitation to Computer Science 6th Edition
Chapter 6
An Introduction to System Software and Virtual Machines

2. Objectives In this chapter, you will learn about: System software
Assemblers and assembly language
Operating systems
Invitation to Computer Science, 6th Edition

3. Introduction Von Neumann computer
“Naked machine”
Hardware without any helpful user-oriented features
Data as well as instructions must be represented in binary
Extremely difficult for a human to work with
To make a Von Neumann computer usable:
Create an interface between the user and the hardware
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4. Introduction (continued)
Tasks of the interface
Hide details of the underlying hardware from the user
Present information in a way that does not require in-depth knowledge of the internal structure of the system
Allow easy user access to the available resources
Prevent accidental or intentional damage to hardware, programs, and data
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5. System Software System software The virtual machine
a collection of compute programs that manage the resources of a computer and facilitate access to those resources
Acts as an intermediary between users and hardware
Creates a virtual environment for the user that hides the actual computer architecture
Software: sequences of instructions that solve a problem
The virtual machine
Set of services and resources created by the system software and seen by the user
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6. Figure 6.1 The Role of System Software
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7. Types of System Software
System software is a collection of many different programs
Operating system
Controls the overall operation of the computer
Communicates with the user
Determines what the user wants
Activates system programs, applications packages, or user programs to carry out user requests
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8. Types of System Software (continued)
Memory managers
Allocate memory space for programs and data
Information managers
Handle the organization, storage, and retrieval of information on mass storage devices
I/O systems
Allow you to easily and efficiently use the input and output devices that exist on a computer system
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9. Types of System Software (continued)
User interface
Provides user with an intuitive visual overview
Graphical user interface (GUI) provides graphical control of the capabilities and services of the computer
Language services (assemblers, compilers, and interpreters)
Allow you to write programs in a high-level, user-oriented language, and then execute them
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10. Types of System Software (continued)
Scheduler
Keeps a list of programs ready to run on the processor and selects the one that will execute next
Utilities
Collections of library routines that provide services either to user or other system routines
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11. Figure 6.2 Types of System Software
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12. 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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13. Assembly Language (continued)
Assembly languages
Designed to overcome shortcomings of machine languages
Create a more productive, user-oriented environment
Earlier termed second-generation languages
Now viewed as low-level programming languages
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14. Assembly Language Assembly language High-level programming languages
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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15. Figure 6.3 The Continuum of Programming Languages
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16. Assembly Language (continued)
Source program
Program written in assembly language
Object program
A machine language program
Assembler
Translates a source program into a corresponding object program
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17. Figure 6.4 The Translation/ Loading/Execution Process
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18. Assembly Language (continued)
Advantages of writing in assembly language rather than machine language
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
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19. 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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20. Figure 6.5 Typical Assembly Language Instruction Set
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21. Invitation to Computer Science, 6th Edition

22. How to declare data in assembly language?
Example: (pseudo-op)
FIVE: .DATA 5
Address content
NEGSEVEN: .DATA -7
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23. How to use data? LOAD FIVE ADD NEGSEVEN
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24. Assembly Language (continued)
Advantages of symbolic labels
Program clarity
Maintainability
Pseudo-op
Invokes the service of the assembler
Provides program construction
.BEGIN
.END
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25. Figure 6.6 Structure of a Typical Assembly Language Program
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26. Invitation to Computer Science, 6th Edition

27. Examples of Assembly Language Code
Algorithmic operations
Set the value of i to 1 (line 2). :
Add 1 to the value of i (line 7).
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28. Examples of Assembly Language Code (continued)
Assembly language translation
LOAD ONE --Put a 1 into register R.
STORE I --Store the constant 1 into i. :
INCREMENT I --Add 1 to memory location i.
I: .DATA The index value. Initially it is 0.
ONE: .DATA The constant 1.
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29. Examples of Assembly Language Code (continued)
Arithmetic expression
A = B + C – 7
(Assume that B and C have already been assigned values)
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30. Examples of Assembly Language Code (continued)
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 The constant 7.
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31. Examples of Assembly Language Code
Conditional operation
Tests and compares values
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32. Examples of Assembly Language Code
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33. Examples of Assembly Language Code (continued)
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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34. Figure 6.8 Assembly Language Program to Compute the Sum of Nonnegative Numbers
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35. Invitation to Computer Science, 6th Edition

36. Invitation to Computer Science, 6th Edition

37. Translation and Loading
Before a source program can be run, an assembler and a loader must be invoked
Assembler
Translates a symbolic assembly language program into machine language
Loader
Reads instructions from the object file and stores them into memory for execution
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38. Translation and Loading (continued)
Assembler: 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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39. 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 (left)
Pass
Process of examining and processing every assembly language instruction in the program, one instruction at a time
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40. Translation and Loading (continued)
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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41. Op Code Table Figure 6.9 Structure of the Op Code Table
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42. First Pass Figure 6.10 Generation of the Symbol Table
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43. 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
Location counter
Variable used to determine the address of a given instruction
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44. Figure 6.11 Outline of Pass 1 of the Assembler
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45. Translation and Loading (continued)
Second pass
Assembler translates source program into machine language
Translate source program into object program.
Eg: SUBSTRACT X
Looks up SUBSTRACT in op code table
Looks up the symbol X in the symbol table
Handle data generation
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46. Translation and Loading (continued)
Second pass
Translate source program into object program.
Handle data generation
Build proper binary representation (sign/magnitude or two's complement)
Eg: LOAD NEGSEVEN …
NEGSEVEN: .DATA -7
After completion of pass 1 and pass 2
Object file contains the translated machine language object program
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47. Figure 6.12 Outline of Pass 2 of the Assembler
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48. Figure 6.13 Example of an Object Program
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51. Operating Systems Operating system System commands
Waits for requests and activates other system programs to service these requests
System commands
Used to translate, load, and run programs
Types of system commands
Lines of text typed at a terminal
Menu items displayed on a screen and selected with a mouse and a button: Point-and-click
Examined by the operating system
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52. Functions of an Operating System
Five most important responsibilities of the operating system
User interface management
Control of access to system and files (security)
Program scheduling and activation
Efficient resource allocation
Deadlock detection and error detection
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53. 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,
Text-oriented
a GUI supports visual aids and point-and-click operations
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54. Figure 6.14 Some Typical Operating System Commands
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55. Responsibility of the Operating System
Figure 6.15 User Interface
Responsibility of the Operating
System
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56. Figure 6.16 Example of a Graphical User Interface
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57. System Security and Protection
Operating system
Non-authorized people from using the computer
User names and passwords
Legitimate users from accessing data or programs they are not authorized to access
Authorization lists
Safeguards password file
Sometimes uses encryption to provide security
Access control
Use of a legal user name and password
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58. Figure 6.17 Authorization List for the File GRADES
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59. 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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60. 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
Program A Program B
Get Data from D Get the laser printer
Get the laser printer Get the data file D
Print the file Print the file
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61. The Safe Use of Resources (continued)
Deadlock prevention
Operating system uses resource allocation algorithms that prevent deadlock from occurring in the first place
If a program cannot get all the resources that it needs, it must give up all the resource it currently owns and issue a completely new request.
Deadlock recovery algorithms
Detect and recover from deadlocks
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62. 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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63. Figure 6.18 Operation of a Batch Computer System
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64. Figure 6.19 Structure of a Typical Batch Job
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65. Historical Overview of Operating Systems Development (continued)
Third-generation operating systems
Multiprogrammed operating systems (1965–1985)
Many user programs are simultaneously loaded into memory
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66. 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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67. Figure 6.20 Configuration of a Time-Shared Computing System
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68. Figure 6.21 A Local Area Network
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69. 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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70. 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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71. Figure 6.23 Structure of a Distributed System
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72. Figure 6.24 Some of the Major Advances in Operating Systems Development
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73. Summary System software Assembly language An assembler
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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74. Java preparation Java download: Eclipse: Free Video Tutorials
Eclipse:
Free Video Tutorials
Invitation to Computer Science, 6th Edition