Operating Systems: Hidden Software
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Transcript of Operating Systems: Hidden Software
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OPERATING SYSTEMSSoftware in the Background
Chapter 2
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Objectives• Describe the functions of an Operating System• Explain the basics of a personal computer operating system• Describe the advantages of a graphical operating system• Differentiate among different versions of Microsoft Windows• Explain the need for network operating systems• Describe the methods of resource allocation on large
computers• Be able to describe the differences among multiprocessing,
multiprogramming, and timesharing• Explain the principles of memory management• List several functions typically performed by utility programs
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Contents• Operating System: Hidden Software• Systems Software• Functions of OS• Types of OS
– MS-DOS– Microsoft Windows– Mac OS– UNIX– LINUX– Network Operating System NOS
• Resource Allocation• Utility Programs
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Operating SystemHidden Software
• Definition – provides access to all resources• Kernel
– Manages the operating system– Memory resident– Loads set of programs that lies between applications
software and the hardware– Fundamental software that controls non-resident portions of
the OS as needed• Booting – Loads the kernel into memory
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Systems Software
• Definition:– All programs related to coordinating
computer operations• Components
– Operating System– Utility programs– Program language translators
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Functions of OS• Manage the computer’s resources
– CPU– Memory– Disk drives– Printers
• Establish a user interface
• Execute and provide services for applications software
• Carries out all input and output operation
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User Interface• Facilitates communication between the user and
the operating system
• Two forms– Command line
• Text-based• Key commands• Examples: MS-DOS, Unix
– Graphical user interface (GUI)• Visual images• Menus• Examples: Windows, Mac OS, Linux
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Platform
• Definition:Computer hardware and operating system software that dictate what other software can run
• WintelIntel-based PC running Microsoft Windows
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OS is Hidden• User interested in application
software to make the PC useful
• Application software is platform specific
• User must be aware of the type of OS
• User should be aware of the functions of OS
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Types of OS
Command line
Single user PC
Network Operating System (NOS)
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MS-DOS
• Command-line interface
• Prompt – system is waiting for you to do something
• Key a command
• Not user-friendly
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Microsoft Windows• Graphical user
interface
• Eases access to the OS
• Most new computers come with Windows already installed
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GUI
• On-screen pictures– Icons– Menus
• Pull down• Pop up
– Click to activate a command or function
• Fast• Easy• Intuitive
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Early Days of Windows
Operating environment for MS-DOS
Shell – layer added between users and DOS
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Windows Today
• Home/consumer market– Windows 95– Windows 98– Windows Millennium Edition (ME)
• Corporate market– Windows NT– Windows 2000
• Windows XP• Pocket computers and Internet appliances
– Windows CE
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Windows 95 and 98• Self-contained OS• DOS commands still available• Start programs by
– Start button– Double clicking the icon
• Task bar permits movement between open programs
• Long file names up to 255 characters• Plug and play• Object linking and embedding (OLE)
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Windows 98 Additions
• Internet / intranet browsing
• Support for DVD and additional multimedia components
• Support for large hard drives
• TV viewer and broadcast ability
• Wizards
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Improved Windows Features
• Backup• Interfaces with other software• Networking features• Security• Dr. Watson
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Windows
Helps reduce the cost of owning and maintaining a PC
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Windows MEMillennium Edition
Multimedia support -- Windows Media Player 7• Jukebox
– Record music CDs as digital files• Windows Movie Maker
– Basic video editing• Windows Image Acquisition
– Scanner and digital camera
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Windows MEMillennium Edition
• Reliability Features– System File Protection– AutoUpdate– System Restore
• Help Center• Home Network Support
– Wizard for connecting multiple computers and peripherals
– Multiple users can share a single Internet connection
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Windows NTNew Technology
• Engineered for stability• Strong security• Versions
– NT Workstation– NT Server
• Drawbacks– Lacks support for older Windows and MS-DOS
software and hardware– Complex to learn and use– Requires more memory and processing power
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Windows 2000
• Stability features• Security features• Uses simple approach to hardware setup
from Windows 98• Versions
– Windows 2000 Professional for individual users– Windows 2000 for network servers
• Was intended for both the corporate and home use, replacing Win NT and Win 98
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Windows 2000
• Complex
• Heavy demand for computer resources
• Improvements over windows NT– Maintains user preferences– Self-healing applications software– Supports Windows 98 file structure– Uses plug and play– Provides improved support for laptops
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Windows XP
• Extends Windows ME and provides a more stable environment
• Two categories – Network server
• 3 versions based upon network complexity – Desktop computer
• 2 versions – Professional Client – Personal Client
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Windows CE Consumer Electronics
Where used• Embedded systems
– Industrial controllers– Robots– Office equipment– Cameras– Telephones– Home entertainment devices– Automobile navigation systems
• Pocket PC• Internet appliance market
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Windows CE Consumer Electronics
Subset of Windows• Less memory
• Smaller screens
• Little or no file storage
• Provides Internet connectivity
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Accessibility Options
• Seeing
• Hearing
• Touching
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Mac OS
• First commercially successful GUI (1984)
• Served as a model to other GUI systems
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UNIX
• Supports– Multi-user– Time-sharing
• Character-based system• Command-line interface• Runs on various processors and many
types of computers• Primary OS used on Internet servers
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LINUX
• UNIX-like OS• Open-source software
– Download it free– Make changes– Distribute copies– Restriction – any changes must be freely available to the
public
• PC Setup– PC comes with Windows installed– Install LINUX in a dual-boot configuration
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LINUX
• Advantages over Windows– Extremely stable– Internet support– Reinstallation is simpler
• Disadvantage– Scarcity of applications
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Network Operating System NOS
• Designed to permit computers on a network to share resources
• Examples– Windows 2000 Server– Novell Net Ware
• Provides– Data security– Troubleshooting– Administrative control
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NOS Functions
• Split between client and server computers• Server
– File management• Client
– Requests to the server– Messaging– Has own local OS
• Makes the resources appear as if they are local to the client’s computer
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Large Computers
• Used by many people at once• OS works “behind the scenes” so users
can share• OS must control
– Who gets access to resources– What keeps the programs from different
users from getting mixed up with one another
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Resource Allocation
• Resource – hardware or software that is needed to complete a task
• Resource Allocation – assigning computer resources to certain programs
• Resource De-allocation – releasing resources when a task is complete
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Allocating the CPU
• One CPU– Multiprogramming
• Event-driven• Timesharing
• More than one CPU– Multiprocessing – multiple CPUs can run
several programs simultaneously
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Multiprogramming
• One CPU• Concurrent execution of two or more
processes– Several processes open at once– Only one process can receive the attention
of the CPU at any given moment– Effective because CPU speeds are many
times faster than input/output speeds
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Event-driven Multiprogramming
• One program receives the attention of the CPU
• Its processing will be interrupted based upon events in the program
• When processing needs to be temporarily suspended, an interrupt is generated
• This is a signal to the operating system to evaluate the cause of the interrupt and determine who should now have CPU time
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Event-driven Multiprogramming Example
• Two programs are running – Payroll and Inventory Management
• Payroll needs to read an employee record
• Payroll generates an interrupt
• Normal processing is temporarily suspended
• The CPU looks at the interrupt and initiates the read operation
• While waiting for the read to complete, the CPU begins processing the Inventory Management program
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Event-driven Multiprogramming Example
• When the read operation is complete, another interrupt is generated
• Normal processing is temporarily suspended
• The CPU looks at the interrupt and determines its cause
• The CPU will either continue processing the Inventory Management program or return to the Payroll program depending upon their priority
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Time-sharing Multiprogramming
• One program receives the attention of the CPU
• A small fraction of CPU time is allocated to the program
• The time slice ends
• The CPU begins processing a different program
• Response time can vary based upon the number of users on the system
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Sharing Memory
• Program must be in memory to be executed
• Problems– Programs compete for space– May have a very large program– Memory space for each program must not
overlap
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Memory Management
• The process of providing separate memory space to programs
• Memory Protection keeps one program from interfering with another
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Memory ManagementMethods
Partitions or regions
Foreground and background
Virtual storage (virtual memory)
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Partitions or Regions
• Divide memory into sections
• The partition must accommodate the largest possible program
• Problem– May cause wasted memory space
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Foreground and Background
• Programs are placed in either Foreground or Background
• Programs in Foreground have priority for CPU time
• While performing read / write operations for the Foreground program, the CPU gives time to a program in Background
• Programs are placed in a holding queue while waiting to run
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Virtual StorageVirtual Memory
Uses concept of Paging
• Divide the program into equal-size pieces (pages)
• Store each piece in equal-size memory spaces (page frames)
• Typical size is 2KB or 4KB
• Create an index to each page and store in a Page Table
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Paging Process
• A portion of the program is placed in memory
• The remainder is on disk
• Sections on disk will be brought into memory as needed (one page at a time)
Virtual StorageVirtual Memory
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Virtual StorageVirtual Memory
• Problem -- Thrashing– Too large a portion of CPU time is spent
locating the correct page and bringing it into memory
• Solution– Run fewer programs concurrently– Add memory
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Memory Protection
• Keeps one program from straying into another• Confines each program to certain defined
limits in memory• Why needed
– Possible for one program to destroy or modify another by transferring to the wrong memory location
– May cause destruction of data• Action if assigned memory space is violated
– Termination of executing program
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Sharing Storage
• Several users need to access the same disk pack– One wants to write– Another wants to read
• OS keeps track of the I/O requests
• OS processes I/O requests in order received
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Sharing Printing Resources
• Print resources are shared between active programs
• Printouts are generated in pieces as the CPU gives each concurrent program some time
• Problem– The current program may generate a few print
lines– The CPU moves to the next program– The second program may generate a few print
lines, etc.
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Sharing Printing Resources
• Result– Printout is worthless as it contains a few lines from
several programs
• Solution – Spooling– Each program thinks it is writing to the printer– The program actually writes to the hard disk– When the program is complete, the file on the hard
disk is sent to the printer
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Additional Printing Problem
• Printers are slow compared to the CPU speed
• Solution– The CPU writing to the disk– The program completes quicker
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Utility Programs
• Come with System Software• Handle special needs• Perform secondary chores• Do not need to be memory resident
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Functions of Utility programs• File manager – provide access to lists of stored files• Backup and Restore – make duplicate copies of
important files and return the copy to the hard drive if needed
• File compression – reduces the amount of disk space required by a file
• Disk defragmenter – reorganize files so they are stored contiguously on disk providing for faster access
• Device drivers – convert operating system instructions into commands that are known to a specific device
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