Chapter 3: Operating Systems: Software in the Background

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Chapter 3Operating Systems Software in the
Background
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Learning ObjectivesYou will be able to describe

• Functions of operating system
• Basics of PC operating system
• Advantages of graphical operating system
• Difference in versions of Windows
• Need for network operating systems

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Learning Objective cont.

• You will be able to describe
• Methods of resource allocation on large computers
• Difference between multiprocessing,
  multiprogramming, and time-sharing
• Principles of memory management
• Functions that are performed by utility programs

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Operating System Hidden Software

• Operating system is a set of programs that lies
  between the applications software and the
  hardware
• Controls access to all other hardware and
  software
• Sometimes used interchangeably with systems
  software, but that is misleading

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Systems Software vs. Operating System

• System software means all programs used to
  control computer operations
• Systems software is comprised of the operating
  system and any utility programs being used to
  control the computer

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Kernel of the Operating System

• The kernel manages the operating system
• Remains in memory at all times, referred to as
  resident
• Controls the operating system and controls
  programs as they are loaded into memory

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Booting the computer

• Booting, from bootstrapping, loads the operating
  system into memory
• When the computer is turned on, a small program
  on the ROM chip runs a small hardware program
  that loads the kernel

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Functions of the operating system

• Managing the computers resources
• Establishes a user interface
• Executes and provides resources for application
  software

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Communicating with the Operating System

• The user communicates with the operating system
  through the user interface
• Two kinds of interfaces
• Command line-user types text commands
• GUI or Graphical User Interface where the user
  interacts with pictures and icons

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Command LineCommon in MS-DOS, Linux, Unix
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GUICommon in Windows and Mac OS
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Personal Computer Operating Systems

• Platform is a combination of computer hardware
  and operating system software
• Most common platforms are Microsoft Windows
  running on Intel based PCs
• Next most common would be Mac OS running on a
  Macintosh computer

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Quick look at MS-DOS

• Command driven operating system
• Text based and waits for instructions at the
  prompt, a signal that the computer is waiting for
  instruction ( C)
• Commands are structured sentences that tell the
  operating system what to do, for example copy a
  file, delete a file, or format at diskette
• Less user-friendly than newer GUI OSs but you
  can still run DOS commands from within Windows

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Microsoft Windows

• Windows is an operating system by Microsoft which
  uses a colorful graphical interface to access the
  operating system
• Most new personal computers (PCs) have a version
  of Windows installed as the operating system

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History of Windows

• Started out as an operating environment which
  means it was a layer between the user and the OS
• Often called a shell because it acts as a coating
  with icons and menus
• Windows 95 was the first version of Windows that
  was a stand alone operating system that did not
  require a DOS installation

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Advantages of Windows

• The GUI environment is easy to use
• Users access the operating system via icons and
  menus
• Clicking the icon or small picture or selecting
  an item from a menu initiates a command or
  function

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Type of Menus

• Pull down menus generally are selected from an
  application toolbar and appear to pull down
• Pop up menus appear from selections at the bottom
  of the screen or from right clicking the mouse
• Start menu is the main menu in Windows that
  allows you to find programs or files

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Plug and Play

• A helpful part of the operating system that
  allows for the addition of new devices such as
  sound cards or scanners
• The operating system detects devices as they are
  plugged in and configures the computer
  automatically to allow instant play

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OLE-Object Linking and Embedding

• Another function of Windows is to allow embedding
  objects in other documents
• For example, you may embed or link a spreadsheet
  in Powerpoint presentation and when you edit that
  portion of the presentation, it will open Excel
  and allow you to edit

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Flavors of Windows

• For the home user, the OS has generally been of
  the Windows 9x series (95, 98) and also Millenium
  edition (ME)
• For the business market, Windows NT and Windows
  2000
• In 2001 Microsoft introduced Windows XP to meet
  the needs of both home users and business users

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What 98 ME brought to the table

• Internet functionality
• Added hardware support (DVD, etc.)
• Multigigabyte disk drives
• TV viewer and broadcast
• Wizards
• Multimedia support
• Reliability features
• Home network support

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Windows NT

• Generally for networked corporate environments
• Looks like Windows 98
• More robust and reliable than home versions
• More difficult to learn and requires more from
  the computer to run

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Windows 2000

• Final version of NT
• Incorporated some of the user-friendliness of 98
  into the NT product
• Supports user indentification allowing more than
  one person to use a computer and maintain their
  personal workspace

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Windows XP

• The newest operating system available from
  Microsoft
• Joins the home and corporate user market
• Two versions
• Professional-intended for networked corporate
  environement
• Home edition-consumer oriented without all of the
  extras in the professional edition

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New Features of XP

• Improved interface
• Improved Multimedia support
• Allows for more personalization
• Multiple user support
• Internet support
• Specialized version, Media Center, allows play of
  DVD, receive and record TV

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Windows CE

• CE stands for consumer electronics
• Designed for the internet appliance market and
  embedded systems
• Embedded systems are devices that integrated into
  other products
• Used on pocket PCs
• Can be used on a variety of products such as
  telephones, digital cameras, etc.

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MAC OS

• Operating system for Apples Macintosh computers
• First commercially successful GUI
• Current version is Mac OS X (ten)
• Good support for multimedia and allows sharing
  with Windows based machines

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UNIX

• Basically a command line operating system
• Developed by ATTs Bell Labs
• Recently added a GUI interface
• Runs on many different types of hardware
• Commonly used to run internet servers

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LINUX

• Unix-like kernel
• Open source
• Any changes made must be made freely available to
  the public
• Can be installed on a PC
• Dual boot allows you to boot the computer into
  Linux or Windows
• Greater stability and recovery but there are very
  few application software programs written for
  Linux

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Operating Systems for Networks

• NOS allows computers on a network to share
  resources (hard drives, printers, etc.)
• Maintains network security
• Seamless integration makes the device being
  shared appear to be part of the users computer

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Some NOSs

• Windows NT Server
• Windows 2000 Server
• Windows 2003 Server (newest Microsoft product)
  supports .NET platform which allows easy web and
  internet development
• Netware from Novell
• UNIX and Linux can also act as NOS

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Operating Systems for Large Computers

• Large computers, or mainframes, are used by many
  people at one time
• Operating system must determine whose program
  gets system resources to run, keeps track of what
  program is where, and how storage is handled
• VMS is an example of a mainframe OS

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Resource Allocation

• Resource allocation is the process of assigning
  computer resources to programs
• Two ways to share the CPU
• Multiprogramming
• Time-sharing
• Similar sounding, multiprocessing refers to a
  computer with more than CPUs

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Multiprogramming

• Two or more programs running at the same time, or
  concurrently
• The programs take turns with the processor.
  They are using the CPU in the same time frame,
  but not in the same instant
• For example, your operating system may use the
  CPU to load your email program while Microsoft
  Word is saving something to disk

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Multiprogramming Continued

• Event driven meaning that certain events in the
  program trigger the beginning and end of the CPU
  usage
• Generally, calculations are completed before CPU
  time is reliquished
• Uses a system of interrupts that is a signal to
  temporarily suspend normal program operation

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Time-Sharing

• A special case of multiprogramming
• Time driven rather than event driven
• When a slice of time is over, the processing
  automatically switches even if the calculation is
  not complete
• Not a noticeable effect on response time, the
  time delay between a typed request or action and
  the computers response

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Memory Management

• Operating systems task of allocation memory
  resources to programs
• Must also work to keep programs in memory
  separate from other programs in memory

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Foreground vs. Background

• Generally determined by priority
• A foreground task many times is interactive (a
  user is using the application live)
• A background task is less important and will many
  times wait for CPU time

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Virtual Storage

• Also called virtual memory
• Programs running are partially stored on hard
  drive and parts are brought into memory as needed
• The part running is said to be in memory or real
  storage, everything else not being used in in
  virtual storage

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More on Virtual Storage

• Paging is a method of storing things in virtual
  storage
• Divides program into equal pieces called pages
  and stores them in a page frame
• Operating system keeps track of all of these
  pages which may not be stored together using the
  page table, a list of locations where pages are
  stored
• Thrashing occurs when too many of the computers
  resources are used for paging and the application
  itself cannot run

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Sharing other resources

• Other shared resources the operating system must
  control is printing and storage
• Spooling is the act of controlling print jobs
  where the print job is printed to disk until it
  can be printed to paper

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Utility Programs

• Usually activities that are preformed at the
  request of the user
• Considered part of the system software not
  necessarily the operating system
• Examples
• File manager with directory structures
• Backup and restore utilities
• Compression
• Defragmenters
• Device drivers