DOS Operating System

1
DOS Operating System

• Davis Rajkumar (6th), Chapter 11

2
Overview

• DOS and its uses
• DOS Characteristics
• File system
• DOS commands
• Command window
• Batch files
• Returning to Windows

3
MS-DOS

• Disk Operating System (DOS)
• MS-DOS Microsoft DOS
• PC DOS 2000 IBM DOS, latest version
• http//www-306.ibm.com/software/os/dos/
• Once was most popular operating system for
  micro-computers
• Text covers MS-DOS because commands still used in
  Command Window

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Uses of DOS

• Understanding heritage of Windows limitation
• Troubleshooting
• Scripting startup activities or launch of console
  programs, such as Java programs

5
DOS Characteristics

• Single user
• Single process no multitasking
• Command line
• Hierarchical file system
• Limited file protectionread-only, hidden
• Limited memory management
• No virtual memory
• Limited to physical memory and overlays
• No user management

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Resident and Transient Routines

• Resident routines stay in memory
• Nucleus, kernel, or supervisor
• IOCS
• File system
• Command processor or shell
• Transient routines stored on disk until
  neededDOS external commands

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Internal vs External Commands

• Internal commands
• BREAK CALL CHCP CHDIR(CD) CLS COPY CTTY DATE
  DEL(ERASE) DIR ECHO EXIT FOR GOTO IF MKDIR(MD)
  PATH PAUSE PROMPT REM RENAME(REN) RMDIR(RD) SET
  SHIFT TIME TYPE VER VERIFY VOL

• External commands
• APPEND.EXE ASSIGN.COM ATTRIB.EXE BACKUP.EXE
  CHKDSK.EXE COMMAND.COM COMP.EXE DEBUG.EXE
  DISKCOMP.COM DISKCOPY.COM DOSKEY.COM DOSSHELL.COM
  EDIT.COM EDLIN.EXE EMM386.EXE EXE2BIN.EXE
  EXPAND.EXE FASTOPEN.EXE FC.EXE FDISK.EXE
  FORMAT.COM GRAFTABLE.COM GRAPHICS.COM HELP.EXE
  JOIN.EXE KEYB.COM LABEL.EXE MEM.EXE MIRROR.COM
  MODE.COM MORE.COM NLSFUNC.EXE PRINT.EXE
  QBASIC.EXE RECOVER.EXE REPLACE.EXE RESTORE.EXE
  SETVER.EXE SHARE.EXE SORT.EXE SUBST.EXE SYS.COM
  TREE.COM UNDELETE.EXE UNFORMAT.COM XCOPY.EXE

Source http//support.microsoft.com/?id71986
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DOS Memory
UMB Upper memory block UMA Upper memory area
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Shell

• DOS command driven
• COMMAND.COM
• One of DOS system files
• DOS shellinterprets and launches commands
• Some commands internal (resident) and others
  external (transient)

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Accessing Peripherals

• DOS system files
• MSDOS.SYS
• IO.SYS
• I/O access uses both system files
• MSDOS.SYS
• Accepts logical I/O requests
• Translates requests to physical I/O commands
• I/O.SYS
• Hardware dependent
• Accepts physical I/O commands
• Communicates commands to basic input/output
  system (BIOS)

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File System

• MSDOS.SYS
• File system for DOS
• Translates logical I/O requests to physical form
• Responsible for directory management
• Allocates disk space using FAT

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File Allocation Table (FAT)

• Allocates disk space in clusters
• 1024 byte cluster
• Two sectors
• Clusters numbered sequentially
• Beginning with zero
• Boot track 0, sector 0
• Address of first cluster of file stored in
  directory
• Clusters form linked listaddress of next cluster
  at end of current cluster
• MSDOS.SYS receives relative bytes for logical I/O
  requests

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Interrupt Processing

• Intel processor relies on electronic signal
  (interrupt) to establish contact with peripheral
  devices
• Hardware senses signal
• Saves key control information for current process
• Starts interrupt handling routine
• Interrupt handler processes interrupt
• Saved process returned to processor

14
Launching Command Window

• Command line interface for Windows
• To access
• Select "Run" option under "Start" button
• Type cmd.exe in input file of dialog box
• OR
• Select "Command Prompt" from Start All Programs
  Accessories menu

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Command Window
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Command Window Utilities

• date display or set date
• time display or set time
• title set title on Command Window
• prompt set prompt in Command Window
• help list all DOS commands
• echo display string or write string to file

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File System

• DOS uses hierarchical file system
• Each storage device has root directory
• C\ -- hard drive
• A\ -- floppy drive
• F\ -- memory stick
• Type drive letter and colon at command prompt to
  change default drive, F
• Each directory can hold directories or files
• Tree command will list directories,
  sub-directories, and files

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Tree of Memory Stick
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Path

• Absolute
• Lists all directories from root to target file
• F\general\MomDad\Receipt\slice.gif
• Relative
• Lists directories from current working directory
• .\Receipt\slice.gif
• This directory "."
• Parent directory ".."

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Path Commands

• path lists current search path
• path PATHnew_path adds path to search path
• subst associates path with drive letter

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Name Restrictions

• Short names
• Eight dot three limit of eight character name
  and three character extension
• 460Files directory name
• DOS_Lab.txt file name
• Legal characters
• Letters and digits A..Z, a..z, and 0..9
• ' ( ) _at_ ! _
• No spaces allowed

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Conventional File Extensions

• ASM - assembler code
• BAK - backup file
• BAS - Basic code
• BAT - batch file
• BIN - binary file
• COB - COBOL code
• COM - command file
• DAT - ASCII data
• DIF - difference file
• DOC - ASCII document
• DVD - device driver

• EXE - executable image
• FOR - FORTRAN code
• LIB - library source
• LST - ASCII list file
• MAP - ASCII load module
• OBJ - object module
• OVR - overlay file
• REF - cross reference
• TMP - temporary link
• - temporary work

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Directory Commands

• cd change directory
• mkdir make new directory in current working
  directory
• rmdir remove a directory
• dir list content of a directory
• tree list directory hierarchy

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File Commands

• type display content of file
• del delete one or more files
• erase delete one or more files
• copy copy one or more files
• move move one or more files
• rename change name of a file

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Batch Files

• ASCII file of DOS commands
• Executable
• Used to script a task
• Execute a Java application
• Installation scripts
• Setting up specialized environments
• AUTOEXEC.BAT executes when system boots

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Pipe

• Pipe connects commands together
• MORE displays screen of data at a time
• DIR lists content of directory
• DIR MORE displays content of directory one
  screen full at a time
• is pipe symbol

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Redirection

• Redirection changes destination of output
• gt is redirection symbol
• dir gt DirList.txt writes list of current
  working directory content to "DirList.txt" file
• dir f\general gtgt DirList.txt appends list of
  f\general directory content to DirList.txt file
• gt creates or overwrites file
• gtgt appends to file

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Returning to Windows

• To exit Command Window graciously,at prompt
  type
• exit

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Summary

• Useful for troubleshooting and scripting in
  Windows
• Limited capabilities
• Single user
• Single task
• Limited memory management
• No user management
• System files MSDOS.SYS IO.SYS
• Resident
• File system and IOCS
• Interrupts provide access to peripheral devices
• DOS uses hierarchical directory structure
• COMMAND.COM provides command line shell
• help lists all DOS commands
• In DOS path use \ to separate directories

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Questions?