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 Naked machine To make a Von Neumann computer usable:
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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4. 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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5. Figure 6.1 The Role of System Software
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6. 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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7. 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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8. Figure 6.2 Types of System Software
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9. 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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10. 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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11. 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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12. 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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13. Figure 6.3 The Continuum of Programming Languages
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14. 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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15. Figure 6.4 The Translation/ Loading/Execution Process
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16. Figure 6.5 Typical Assembly Language Instruction Set
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17. 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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18. Figure 6.6 Structure of a Typical Assembly Language Program
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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. How to declare data in assembly language?
Example: (pseudo-op)
FIVE: .DATA 5
Address content
NEGSEVEN: .DATA -7
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21. How to use data? LOAD FIVE ADD NEGSEVEN
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22. 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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23. 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 The constant 7.
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24. 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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25. 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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26. Figure 6.7 Algorithm to Compute the Sum of Numbers
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27. Figure 6.8 Assembly Language Program to Compute the Sum of Nonnegative Numbers
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28. 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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29. 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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30. Figure 6.9 Structure of the Op Code Table
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31. Figure 6.10 Generation of the Symbol Table
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32. 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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33. 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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34. 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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35. Figure 6.11 Outline of Pass 1 of the Assembler
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36. Figure 6.12 Outline of Pass 2 of the Assembler
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37. Figure 6.13 Example of an Object Program
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38. 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
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39. 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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40. Figure 6.14 Some Typical Operating System Commands
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41. Responsibility of the Operating System
Figure 6.15 User Interface
Responsibility of the Operating
System
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42. Figure 6.16 Example of a Graphical User Interface
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43. 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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44. Figure 6.17 Authorization List for the File GRADES
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45. 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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46. 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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47. 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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48. 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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49. 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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50. Figure 6.18 Operation of a Batch Computer System
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51. Figure 6.19 Structure of a Typical Batch Job
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52. 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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53. 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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54. Figure 6.20 Configuration of a Time-Shared Computing System
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55. Figure 6.21 A Local Area Network
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56. 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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57. 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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58. Figure 6.23 Structure of a Distributed System
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59. Figure 6.24 Some of the Major Advances in Operating Systems Development
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60. 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
Invitation to Computer Science, 6th Edition