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Mercy Lou H. Yecla
MS-DOS
o History
o Design Goals
o Memory Management
o Processor Management
o Device Management
o File Management
o User Interface
o Additional Commands
MS-DOS, PC-DOS or DOS:
        Microsoft Disk Operating System
o Developed to run single-user, stand-alone desktop
  computers.
    Exemplifies early Operating Systems because it manages jobs
     sequentially from single user.
o Advantages: Simple operation & straight-forward user
  commands.
o Disadvantages:
   1. Lack of flexibility & limited ability to meet needs of programmers
      & experienced users.
   2. Written for a single family of microprocessors (Intel family of
      chips: 8086, 8088, 80186, and 80286).
History of DOS
History of DOS (cont)
Design Goals
o Accommodate single novice user in single-
  process environment.
o Standard I/O support includes keyboard,
  monitor, printer, & secondary storage unit.
o User commands are based on English
  words/phrases indicative of action to be
  performed.
o Commands are interpreted by command
  processor.
o Layering approach “protects” user from
  hardware.
MS-DOS Architecture
              User




       COMMAND.COM


          DOS Kernel   MS-DOS

               BIOS




        Hardware
First 2 DOS Layers : BIOS &
            Kernel
• BIOS (Basic Input/Output System) -- interfaces directly with various I/
  O devices.
       Device drivers (control flow of data to/from each device).
       Receives status info about success/failure of each I/O operation & passes
        it on to the processor.
• DOS kernel -- routines needed to interface with the disk drives.
       Read into memory at initialization time from MSDOS.SYS file on boot
        disk.
       Accessed by application programs.
       Provides a collection of hardware-independent services, such as memory
        management, & file & record management (system functions).
Third DOS Layer : Command
        Processor

3. Command processor (shell) -- sends prompts to user,
   accepts commands, executes commands, & issues
   appropriate responses.
    Resides in a file called COMMAND.COM, which consists of 2 parts stored
     in 2 different sections of main memory.
    Not interpretive.
    MS-DOS Version 4.0 -- menu-driven DOS shell.
    OS/2 -- designed to replace MS-DOS.


o MS-DOS ran enormous collection of software packages
  making it difficult to discontinue.
DOS Memory Management


o Memory Manager
  – Relatively simple job because it’s managing single
    job for single user.
  – Uses a first-fit memory allocation scheme since it
    is most efficient strategy in a single-user
    environment.
DOS Main Memory
       Allocation
o First versions had simple contiguous memory allocation scheme that
  gave all of the available memory to resident application program.
    Applications couldn’t dynamically allocate memory blocks.
    MS-DOS Version 2.0 supported dynamic allocation, modification, & release of main
     memory blocks by applications.
o Amount of memory each application owns depends on type of file from
  which program is loaded & size of TPA.
    Programs.COM -- given all of TPA, whether or not they need it.
    Programs.EXE -- given amount of memory they need.
Memory Block Allocation

o Allocates memory by using first-fit algorithm & linked list of
  memory blocks.
o With Version 3.3, MS-DOS started using best-fit or last-fit
  strategy.
o Size of a block can vary from 16 bytes (paragraph) to maximum
  available memory.
Free/Busy Block List

o Whenever request for memory comes in, DOS looks through free/busy
  block list to find free block that fits.
    If list becomes disconnected, system stops & must be rebooted.
o Well-designed application program releases memory block it no longer
  needed.
Process Management

o MS-DOS doesn’t support multitasking.
   Programs can’t break out of middle of DOS internal
    routine & restart routine from somewhere else.
   There's no interleaving & no need for sophisticated
    algorithms or policies to determine which job will run next
    or for how long.
Interrupt Handlers

o Interrupt Handlers - are Responsible for Synchronizing Processes
o PC has 256 interrupts & interrupt handlers, & they are accessed via
  interrupt vector table.
o Three types of interrupts:
• Internal hardware interrupts -- generated by certain events occurring
  during program’s execution (e.g., division by zero).
• External hardware interrupts -- caused by peripheral device controllers
  or by coprocessors & assigned by manufacturers.
• Software interrupts -- generated by system & application programs to
  access DOS & BIOS functions, which, in turn, access system resources.
Interrupt Handlers (cont)
• Software interrupts (continued)
  – Some activate specialized application programs
     • Take control of computer
     • Example: Borland’s SideKick (type of TSR)
  – Terminate and Stay Resident (TSR) interrupt handler
     •   Terminates process without releasing memory
     •   Used by subroutine libraries
     •   Sets up memory tables
     •   Execution preparation via DOS interrupt connection
     •   Determines memory required
     •   Sends return code back to parent
Interrupt Handlers (cont)
• Interrupt synchronization
  – CPU senses interrupt
     • Puts on stack: contents of PSW (program status word),
       code segment register, and instruction pointer register
     • Disables interrupt system
     • Uses eight-bit number to obtain interrupt handler
       address
     • Interrupt handler reenables interrupt system: allows
       higher-priority interrupts to occur
     • Saves registers and processes interrupt
Device Management

o Ability to reorder requests to optimize seek & search time is not a feature
  of DOS because it’s designed for a single-user environment.
    All requests are handled on a first-come first-served basis.
    Since version 3.0, BIOS can support spooling so users can schedule
      several files to be printed one after the other.
o MS-DOS written for simple systems using keyboard, monitor, printer,
  mouse, 1-2 serial ports, & maybe second printer.
    Devices do not require special management from OS.
    Device drivers are the only items needed by Device Manager to make
      system work.
    A device driver is a software module that controls an I/O device and
      handles its interrupts.
Managing Files

o   Earliest versions of MS-DOS kept every file in a single directory.
o   Version 2.0 implemented hierarchical directory structure.
o   When disk is formatted, its tracks are divided into sectors of 512 bytes.
o   2-8 sectors are grouped into clusters & that's how File Manager allocates
    space to files.
FORMAT Creates Three
     Special Areas on Disk
•   Boot record -- first sector of every logical disk & contains disk boot
    program & table of disk's characteristics.

•   Root directory -- Lists system’s primary subdirectories & files (name,
    extension, size, date & time of modification, starting cluster #, file
    attribute codes).

•   FAT (File Allocation Table) -- contains status info about disk’s sectors:
    which are allocated, which are free, and which can’t be allocated
    because of errors.
Managing Files in DOS

o Supports noncontiguous file storage & dynamically allocates
  disk space to a file, provided there’s enough disk room.
o Compaction (MS-DOS Version 6.0) available via utility used to
  defragment disk (DEFRAG.EXE).
o CHKDSK command used to determine need for compaction.
o Restricting user access to computer system & resources isn’t
  built into MS-DOS.
User Interface
o Command-driven operating system.

o When user presses Enter key, shell (COMMAND.COM)
  interprets command & calls on next lower level routine to
  satisfy request.

o User commands include some or all of these elements in this
  order:
command source-file destination-file switches
Batch Files & Redirection

o By creating customized batch files, users can quickly execute
  combinations of DOS commands to configure their system,
  perform routine tasks, or make it easier for non-technical
  users to run software.

o MS-DOS can redirect output from one standard input or
  output device to another.
      command > destination
      E.g., dir > PRN
Filter Commands
             (SORT, MORE)
o Filter commands accept input from default device, manipulate data in
  some fashion, & send results to default output device.

o SORT accepts input from keyboard, sorts that data, & displays it on
  screen.
     Sort the file by column.

o MORE causes output to be displayed on screen in groups of 24 lines,
  one screen at a time, & waits until user presses Enter key before
  displaying next 24 lines.
Pipe
• Cause standard output from one command to be used as standard
  input to another command.
    – Symbol is a vertical bar, |.
    – Alphabetically sort directory & display sorted list on screen:
         DIR | SORT


• Combine pipes and other filters.
        TYPE INVENTRY.DAT | MORE
        MORE < INVENTRY.DAT
        DIR | SORT | MORE
        DIR | SORT > SORTFILE
        MORE < SORTFILE
Summary
• MS-DOS
  – Written to serve 1980s personal computer users
• Limitation
  – Limited flexibility
  – Operating system unusable as hardware evolved
• First standard operating system
  – Adopted by personal computing machine
    manufacturers
  – Supported by legions of software design groups
Summary (continued)
• Advantages
  – Fundamental operation
  – Straightforward user commands
• Weakness
  – Design
     • Single-user/single-task systems
  – No multitasking, networking, sophisticated
    applications support

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Ms dos

  • 1. Mercy Lou H. Yecla
  • 2. MS-DOS o History o Design Goals o Memory Management o Processor Management o Device Management o File Management o User Interface o Additional Commands
  • 3. MS-DOS, PC-DOS or DOS: Microsoft Disk Operating System o Developed to run single-user, stand-alone desktop computers.  Exemplifies early Operating Systems because it manages jobs sequentially from single user. o Advantages: Simple operation & straight-forward user commands. o Disadvantages: 1. Lack of flexibility & limited ability to meet needs of programmers & experienced users. 2. Written for a single family of microprocessors (Intel family of chips: 8086, 8088, 80186, and 80286).
  • 5. History of DOS (cont)
  • 6. Design Goals o Accommodate single novice user in single- process environment. o Standard I/O support includes keyboard, monitor, printer, & secondary storage unit. o User commands are based on English words/phrases indicative of action to be performed. o Commands are interpreted by command processor. o Layering approach “protects” user from hardware.
  • 7. MS-DOS Architecture User COMMAND.COM DOS Kernel MS-DOS BIOS Hardware
  • 8. First 2 DOS Layers : BIOS & Kernel • BIOS (Basic Input/Output System) -- interfaces directly with various I/ O devices.  Device drivers (control flow of data to/from each device).  Receives status info about success/failure of each I/O operation & passes it on to the processor. • DOS kernel -- routines needed to interface with the disk drives.  Read into memory at initialization time from MSDOS.SYS file on boot disk.  Accessed by application programs.  Provides a collection of hardware-independent services, such as memory management, & file & record management (system functions).
  • 9. Third DOS Layer : Command Processor 3. Command processor (shell) -- sends prompts to user, accepts commands, executes commands, & issues appropriate responses.  Resides in a file called COMMAND.COM, which consists of 2 parts stored in 2 different sections of main memory.  Not interpretive.  MS-DOS Version 4.0 -- menu-driven DOS shell.  OS/2 -- designed to replace MS-DOS. o MS-DOS ran enormous collection of software packages making it difficult to discontinue.
  • 10. DOS Memory Management o Memory Manager – Relatively simple job because it’s managing single job for single user. – Uses a first-fit memory allocation scheme since it is most efficient strategy in a single-user environment.
  • 11.
  • 12. DOS Main Memory Allocation o First versions had simple contiguous memory allocation scheme that gave all of the available memory to resident application program.  Applications couldn’t dynamically allocate memory blocks.  MS-DOS Version 2.0 supported dynamic allocation, modification, & release of main memory blocks by applications. o Amount of memory each application owns depends on type of file from which program is loaded & size of TPA.  Programs.COM -- given all of TPA, whether or not they need it.  Programs.EXE -- given amount of memory they need.
  • 13. Memory Block Allocation o Allocates memory by using first-fit algorithm & linked list of memory blocks. o With Version 3.3, MS-DOS started using best-fit or last-fit strategy. o Size of a block can vary from 16 bytes (paragraph) to maximum available memory.
  • 14. Free/Busy Block List o Whenever request for memory comes in, DOS looks through free/busy block list to find free block that fits.  If list becomes disconnected, system stops & must be rebooted. o Well-designed application program releases memory block it no longer needed.
  • 15. Process Management o MS-DOS doesn’t support multitasking.  Programs can’t break out of middle of DOS internal routine & restart routine from somewhere else.  There's no interleaving & no need for sophisticated algorithms or policies to determine which job will run next or for how long.
  • 16. Interrupt Handlers o Interrupt Handlers - are Responsible for Synchronizing Processes o PC has 256 interrupts & interrupt handlers, & they are accessed via interrupt vector table. o Three types of interrupts: • Internal hardware interrupts -- generated by certain events occurring during program’s execution (e.g., division by zero). • External hardware interrupts -- caused by peripheral device controllers or by coprocessors & assigned by manufacturers. • Software interrupts -- generated by system & application programs to access DOS & BIOS functions, which, in turn, access system resources.
  • 17. Interrupt Handlers (cont) • Software interrupts (continued) – Some activate specialized application programs • Take control of computer • Example: Borland’s SideKick (type of TSR) – Terminate and Stay Resident (TSR) interrupt handler • Terminates process without releasing memory • Used by subroutine libraries • Sets up memory tables • Execution preparation via DOS interrupt connection • Determines memory required • Sends return code back to parent
  • 18. Interrupt Handlers (cont) • Interrupt synchronization – CPU senses interrupt • Puts on stack: contents of PSW (program status word), code segment register, and instruction pointer register • Disables interrupt system • Uses eight-bit number to obtain interrupt handler address • Interrupt handler reenables interrupt system: allows higher-priority interrupts to occur • Saves registers and processes interrupt
  • 19. Device Management o Ability to reorder requests to optimize seek & search time is not a feature of DOS because it’s designed for a single-user environment.  All requests are handled on a first-come first-served basis.  Since version 3.0, BIOS can support spooling so users can schedule several files to be printed one after the other. o MS-DOS written for simple systems using keyboard, monitor, printer, mouse, 1-2 serial ports, & maybe second printer.  Devices do not require special management from OS.  Device drivers are the only items needed by Device Manager to make system work.  A device driver is a software module that controls an I/O device and handles its interrupts.
  • 20. Managing Files o Earliest versions of MS-DOS kept every file in a single directory. o Version 2.0 implemented hierarchical directory structure. o When disk is formatted, its tracks are divided into sectors of 512 bytes. o 2-8 sectors are grouped into clusters & that's how File Manager allocates space to files.
  • 21. FORMAT Creates Three Special Areas on Disk • Boot record -- first sector of every logical disk & contains disk boot program & table of disk's characteristics. • Root directory -- Lists system’s primary subdirectories & files (name, extension, size, date & time of modification, starting cluster #, file attribute codes). • FAT (File Allocation Table) -- contains status info about disk’s sectors: which are allocated, which are free, and which can’t be allocated because of errors.
  • 22. Managing Files in DOS o Supports noncontiguous file storage & dynamically allocates disk space to a file, provided there’s enough disk room. o Compaction (MS-DOS Version 6.0) available via utility used to defragment disk (DEFRAG.EXE). o CHKDSK command used to determine need for compaction. o Restricting user access to computer system & resources isn’t built into MS-DOS.
  • 23. User Interface o Command-driven operating system. o When user presses Enter key, shell (COMMAND.COM) interprets command & calls on next lower level routine to satisfy request. o User commands include some or all of these elements in this order: command source-file destination-file switches
  • 24.
  • 25. Batch Files & Redirection o By creating customized batch files, users can quickly execute combinations of DOS commands to configure their system, perform routine tasks, or make it easier for non-technical users to run software. o MS-DOS can redirect output from one standard input or output device to another. command > destination E.g., dir > PRN
  • 26. Filter Commands (SORT, MORE) o Filter commands accept input from default device, manipulate data in some fashion, & send results to default output device. o SORT accepts input from keyboard, sorts that data, & displays it on screen.  Sort the file by column. o MORE causes output to be displayed on screen in groups of 24 lines, one screen at a time, & waits until user presses Enter key before displaying next 24 lines.
  • 27. Pipe • Cause standard output from one command to be used as standard input to another command. – Symbol is a vertical bar, |. – Alphabetically sort directory & display sorted list on screen: DIR | SORT • Combine pipes and other filters. TYPE INVENTRY.DAT | MORE MORE < INVENTRY.DAT DIR | SORT | MORE DIR | SORT > SORTFILE MORE < SORTFILE
  • 28. Summary • MS-DOS – Written to serve 1980s personal computer users • Limitation – Limited flexibility – Operating system unusable as hardware evolved • First standard operating system – Adopted by personal computing machine manufacturers – Supported by legions of software design groups
  • 29. Summary (continued) • Advantages – Fundamental operation – Straightforward user commands • Weakness – Design • Single-user/single-task systems – No multitasking, networking, sophisticated applications support

Editor's Notes

  1. Figure are the layer structured of a ms-dos