1. External Commands
Are stored in some external files which are stored on some secondary storage device.
Whenever an external command is executed then the external file in which that particular command is stored in transferred from disk to main memory i.e. RAM
All executable files with extensions .com, .exe and .bat are the external commands.

2. Where the DOS external files resides?
C:\> cd WINDOWS C:\>WINDOWS> CD COMMAND C:\> WINDOWS> COMMAND> dir In Windows7 C:\>WINDOWS> CD SYSTEM32 C:\> WINDOWS> SYSTEM32 > dir

3. ATTRIB Change or view the attributes of one or more files.
Stored in ATTRIB.EXE file which is needed for its execution.
Syntax:
ATTRIB [+R|-R] [+A|-A] [+S|-S] [+H|-H][drive:][path][filename] [/S [/D]]
Options:
To add an attribute attach a '+' in front of it.
To remove an attribute attach a '-' in front of it
Attributes include
R - Read-only
A - Archive
S - System
H - Hidden
/D - Process folders as well.
/S - Process matching files in the current folder and all subfolders.

4. ATTRIB: EXAMPLES C:\>attrib
Shows the current attributes of all the files present at C drive.
C:\>attrib abc +H
hides the abc file.
C:\>test +H +R
hides and make the test file read only.

5. LABEL Requires LABEL.EXE file for its execution.
Label is used to view or change the label of the computer disk drives.
Syntax:
LABEL [drive:][label]
Example:
C:\>label a: mydisk
This would label the disk currently in the drive to "mydisk“.

6. BACKUP
External command that requires BACKUP.EXE for executing this command.
Enables users to backup their data on their computer.
Syntax:
BACKUP [Source:\Path\Filename] [Target:] [/s] [/m] [/a] [/d:date] [/t:time] [/f:size] [/L:LogDrive:\Path\Log]

7. BACKUP OPTIONS /A Does not erase the files on the target disk .
/F:(size)
Formats the target disk (if it is not already formatted). /L
Makes an entry in the backup log in the file you specify here. /M
Only backs up files that have been modified since the last time the BACKUP command was used. /S
Causes files in the specified directory and all subdirectories below the specified directory to be backed up.
/D:(date)
Backs up files only if they have been created or modified on or after the date you enter.
/T:(time)
Backs up files only if they have been created or modified on or after the time you enter.

8. BACKUP: Examples C:\>backup C:\TC F:/S
Copies all the files with all subdirectories of the TC directory to drive F.
C:\>backup c:\letters\sale*.* a:
All files in the drive C LETTERS directory that begin with SALE and with any filename extension are backed up onto the disk in drive A.

9. CHKDSK Requires CHKDSK.EXE file for execution.
Chkdsk is a utility that checks the computer's hard disk drives' status for any cross-linked or any additional errors with the hard disk drive.
Syntax:
CHKDSK [drive:][[path]filename] [/F] [/V]

10. CHKDSK Options /F Fixes errors on the disk. /V
Displays the full path and name of every file on the disk

11. CHKDSK: Examples C:\>chkdsk checks the current drive.
C:\>chkdsk a:
checks the drive a.

12. FORMAT Requires an external file FORMAT.COM.
Used to make a disk usable for OS by dividing the disk into magnetic tracks and sectors.
Syntax:
FORMAT drive:/switches

13. FORMAT Options /V[:label] Specifies the volume label. /Q
Performs a quick format.
/F:size
Specifies the size of the floppy disk to format (such as 160, 180, 320, 360, 720, 1.2, 1.44). /B
Allocates space on the formatted disk for system files. /S
Copies system files to the formatted disk.
/T:tracks
Specifies the number of tracks per disk side.
/N:sectors
Specifies the number of sectors per track. /1
Formats a single side of a floppy disk. /8
Formats eight sectors per track. /C
Tests clusters that are currently marked "bad."

14. FORMAT: Examples C:\>format A: formats a disk A. C:\>format A:/3
formats 31/2 inch floppy disk.

15. MOVE Executed when a file MOVE.EXE is loaded in RAM.
Used to move one or more files.
Analogous to cut and paste.
Syntax: MOVE <source> <destination>

16. MOVE Options /Y
Suppresses prompting to confirm you want to overwrite an existing destination file.
/-Y
Causes prompting to confirm you want to overwrite an existing destination file.

17. MOVE: Examples C:\>move c:\windows\temp\*.* c:\temp
Moves the files of c:\windows\temp to the temp directory in root, this is of course assuming you have the windows\temp directory.
C:\>move abc test
renames the abc directory to test.

18. TREE Displays all the directories and subdirectories graphically.
Syntax
TREE <path> /switches
Options /F
Includes the file names in each subdirectory. /A
Displays the subdirectory using standard ASCII characters rather than graphic characters .

19. TREE: Example
D:\>tree tc

20. DELTREE Requires external file DELTREE.EXE for its execution.
Deletes a directory and all the subdirectories and files in it.
Syntax:
DELTREE [/Y] [drive:]path [[drive:]path[...]]

21. DELTREE: Examples C:\>deltree c:\fake010
Deletes the fake010 directory and everything in it.
C:\>deltree D:\test\*.*
Deletes all the files in test directory present on drive D.

22. FIND Requires an external file FIND.EXE.
A filter to find lines in the input data stream that contain or don't contain a specified string and send these to the output data stream.
Syntax
find "keyword" <filename>
Searches for a text string in a file or files.

23. Find Options /V
Displays all lines NOT containing the specified string. /C
Displays only the count of lines containing the string. /N
Displays line numbers with the displayed lines. /I
Ignores the case of characters when searching for the string.

24. FIND: Examples C:\>find “this” def.txt
searches the string this in the def.txt file.
C:\>find “this” def.txt/c
displays the count of lines in def.txt file that contain string this.
C:\>find “this” def.txt/n
Displays the line number which contains this as a string in def.txt.
C:\>dir|find def
Displays whether the file def is there in the current path or not.

25. RESTORE
Used to restore files from disks made using the BACKUP command.
Syntax:
RESTORE sourcedrive: targetdrive: [path][/switches]

26. Restore Options
/P   
The program prompts you before it restores files that have been changed since the last backup or files that are marked read-only.
/S   
Backed up files from both the specified source directory and from subdirectories within that directory are transferred to the target path designation
/B:mm-dd-yy   
Only restores files that were modified on or BEFORE the date you enter.
/A :mm-dd-yy
Only restores files that were modified on or AFTER the date you enter.
/E   
Only restores files that were modified at or EARLIER than the time you enter.
/L  
Only restores files that were modified at or LATER than the given time.
/M   
Only restores files that have been modified since the last backup.
/N   
Only restores files that no longer exist on the destination disk.
/D   
Displays a list of the files on the backup disk that match the names specified in filename without restoring any files

27. RESTORE: Example C:\>restore A: C:
restores files from the backup disk in drive A: that originally resided on the currently logged subdirectory.

28. SORT Sorts input and sends it to the screen or to a file. Syntax
SORT [/R][/+n] <filename>
Options /R
Reverses the sort (sorts from Z to A).
/+n
Starts sorting with column number (n) you enter.

29. SORT: Examples C:\>sort a:test d:abc
To sort the file test on drive A and send the output to a new file abc on drive D.
C:\> sort /r a:phones.txt c:phone1
Sorts in reverse order (Z to A) the file PHONES.TXT on drive A and send the output to a new file PHONE1 on drive C.
C:\> sort /+3 > b:temp Create a sorted file TEMP, sorting on the character in column three, by using input from the keyboard.

30. SYS
Copies MS-DOS system files and command interpreter to a disk you specify.
Syntax:
SYS [drive1:][path] drive2:
Example:
C:\>sys a:
If you type this from c drive and you have a formatted disk in the drive, this would copy the system files to that disk making that disk bootable.

31. DISKCOMP Compares the contents of two disks on a track by track basis.
It checks whether two disks are identical or not.
Compares only floppy disks that are of same size.
Syntax:
DISKCOMP <Source> <Target> /switches
Options:
/1 Compares only the first side of the disks
/8 Compares the first 8 sectors per track.

32. SCANDISK
Requires two external files SCANDISK.EXE and SCANDISK.INI for execution.
Disk analysis and repair tool used to check a drive for errors and correct any problems that it finds.
Syntax
SCANDISK <drivename>/switches

33. SCANDISK Options /all Used to check and repair all local drives.
/autofix
This option will fix any errors it encounters without prompting you first
/checkonly
Use this option if you want to check a drive for errors without repairing the damage.

34. DISKCOPY Requires an external file DISKCOPY.EXE for its execution.
Used to copy all the files as well as directories from one disk to another on a track by track basis.
Only copy floppy disks that are of the same size and capacity.
If target disk is unformatted, DISKCOPY will automatically format the disk first automatically.
Syntax
DISKCOPY [drive1: [drive2:]]/switches

35. DISKCOPY Options /1
Copies only the first side of the diskette, even if the target diskette is double sided. /V
Verifies that the source data was copied correctly onto the destination drive. Selecting this option will slow down the copying process. /M
Make use of RAM to speed up copy access.

36. DISKCOPY Examples DISKCOPY a: b:
Copies the contents of the disk in drive A to the disk in drive B (erasing any data already on the disk).
DISKCOPY a: a:
If there is only one floppy drive then DOS first reads the source floppy disk and then prompts you to remove the disks and insert the target disk.

37. XCOPY Requires an external file XCOPY.EXE Copy entire directory trees.
Xcopy is a version of the copy command that can move files and directories from one location to another.
Syntax:
xcopy <source_dir> <destination_dir>

38. XCOPY Options /A
Copies only files with the archive attribute set, doesn't change the attribute. /M
Copies only files with the archive attribute set, turns off the archive attribute.
/D:m-d-y
Copies files changed on or after the specified date. If no date is given, copies only those files whose source time is newer than the destination time. /P
Prompts you before creating each destination file. /S
Copies directories and subdirectories except empty ones. /E
Copies directories and subdirectories, including empty ones. Same as /S /E. May be used to modify /T.

39. XCOPY Options Verifies each new file. /V
Prompts you to press a key before copying. /C
Continues copying even if errors occur. /I
If destination does not exist and copying more than one file, assumes that destination must be a directory. /Q
Does not display file names while copying. /F
Displays full source and destination file names while copying. /L
Displays files that would be copied. /H
Copies hidden and system files also. /R
Overwrites read-only files. /T
Creates directory structure, but does not copy files. Does not include empty directories or subdirectories. /T /E includes empty directories and subdirectories.

40. XCOPY: Examples C:\>XCOPY abc\*.txt D:
copies all files in the abc directory with the extension .txt to drive D:
C:\> xcopy c: a: /s
Copies all files and directories (except empty directories) from drive C to drive A.

41. DOSKEY
MS-DOS utility that allows a user to keep a history of commands used on the computer.
Before using it, it is required to install doskey by writing this command on the DOS prompt.
Syntax
doskey/options

42. DOSKEY Options /HISTORY Displays all commands stored in memory
/LINE: size
Sets maximum size of line edit buffer(default:128)
/OVERSTRIKE
Overwrites new characters onto line when typing(default)
/REINSTALL
Installs a new copy of DOSKey
UP,DOWN
arrows recall commands
Esc
clears current command F7
displays command history
Alt+F7
clears command history
[chars]F8
searches for command beginning with [chars] F9
selects a command by number

43. DOSKEY Examples C:\>doskey
installs doskey and allows you to press the up or down command to see history, or right or left to retype previous command.
C:\>doskey /H
Displays a list of all the commands currently stored in memory.

44. DEFRAG
Optimizes disk performance by reorganizing the files on the disk.
Syntax:
defrag Drive: /F /U /S:order /B /Skiphigh /LCD /BW /G0 /A /H

45. DEFRAG Options Option Description Drive:
Drive letter that you wish to defragment. /F
Insures that no empty space remains between files. /U
Leaves empty space if any is found between files.
/LCD
Start defrag in LCD color mode.
/BW
Start defrag in black and white color mode
/G0
Disable mouse and character set /A
Start defrag in automatic mode. /H
Move hidden files.

46. DEFRAG Options Option Description /S
Order/Sorts files in specific sort <order>.
N =Alphabetic name order.
-N= Reverse alphabetic name order.
E =In alphabetic file extension order.
-E =Reverse alphabetic file extension order.
D= In date order (earliest to latest).
-D= Reverse date order (old to new).
S =By file size (small to large)
-S =By file size (large to small) /B
Reboot computer after completing defrag

47. EDIT Requires an external file EDIT.COM for its execution.
Used to create a file, change or modify the contents of an already existing file.
A menu driven text editor.
Syntax:
EDIT filename.extension [/switches]

48. EDIT Switches /B Black and white display. /H
Alerts line display for current monitor. /R
Load file in read only mode.

49. Batch Files An ASCII text file containing a list of DOS commands.
A batch file can be given any valid DOS file name having an extension .BAT
Can be created by using COPYCON command.
COPY CON filename.BAT OR
EDIT filename.BAT

50. Commands Command Description @
Does not echo back the text after the at symbol. This is most commonly used OFF to prevent any of the commands in the batch file from being displayed, just the information needed. %1
The percent followed by a numeric value, beginning with one, allows users to add variables within a batch file. For example,
ECHO Hello %1
When the above one-line batch file is created, add your name after the batch file. For example, typing myname (being the name of the bat file) and then your name:
myname bob
would output:
Hello bob
PAUSE
Prompt the user to press any key to continue.

51. Commands Command Description ::
One of two ways of adding remarks into the batch file without displaying or executing that line when the batch file is run.
:LABEL
By adding a colon in front of a word, such as LABEL, you create a category, more commonly known as a label. This allows you to skip to certain sections of a batch file such as the end of the batch file. Also see GOTO.
CALL
This is used to run another batch file within a batch file. When the batch file that is called is completed, the remainder of the original batch file is completed. Note if the batch file does not exist it will give an error message.
CHOICE
It allows to accept various user responses from a list of options.
CLS
Just like the DOS command would clear your screen.

52. Commands Command Description ECHO
Will echo a message in the batch file. Such as ECHO Hello World will print Hello World on the screen when executed.
EXIT
Exits out of the DOS window if the batch file is running from Windows.
GOTO LABEL
Used to go to a certain label, such as LABEL. An example of GOTO would be to GOTO END IF
Used to check for a certain condition if the condition exists. If that condition exists it will perform that function
REM
One of two ways of adding remarks into the batch file without displaying or executing that line when the batch file is run.
SHIFT
Changes the position of replaceable parameters in a batch program.

53. Simple Batch File
C:\ edit ex.bat date time vol dir/p Save the contents. To execute write C:\>ex.bat

54. Use of ECHO
C:\ edit ex1.bat date pause rem date command is executed. echo ******************** echo echo Hello Everyone echo ********************* rem finishesd

55. To Make and Change Directory
:: makes and changes to the specified directory off Cls MD %1 CD %1

56. To copy all or specified files from the D drive to the current directory
::copies all or specified files from the ::D drive to the current directory off echo if "%1"=="" xcopy D:\*.* if not"%1"=="" xcopy D:\%1 dir

57. IF EXIST command sequence
:: Example of IF EXIST command OFF IF EXIST %1 ECHO File %1 exists! IF EXIST %2 ECHO File %2 exists! IF EXIST %3 ECHO File %3 exists!

58. Pause Command
:: Example of the PAUSE command :: and the ways to exit out of a OFF ECHO The next command is a PAUSE ECHO Do NOT press Ctrl+C or Ctrl+Break PAUSE ECHO Press Ctrl+C or Ctrl+Break PAUSE

59. Looping in Batch Files :: A batch file example using a batch loop.
:TOP DIR GOTO TOP

60. Using variables
@echo off set name=%1 set address=%2 set city=%3 echo My name is %name% echo My address is %address% echo My hometown is %city%

61. Configuring the System

62. CONFIG.SYS
CONFIG.SYS is an ASCII text file that contains instructions to DOS regarding your system configuration.
Resides on the root directory of the default starting drive and is read only once at the startup time.

63. CONFIG.SYS Commands Buffer
Specifies the size of the disk buffer. The disk buffer is the reserved area of RAM for the disk read and write operations.
Syntax:
Buffer=##n
where ## represents numbers between 1-99 and n represents read-ahead buffers which store data just beyond the area of the disk being read.
Example:
Buffer=20

64. CONFIG.SYS Commands Install
Used to install some executable programs after starting of the computer.
This command speeds installation and minimizes addressing problems.
Example:
install=abcd.exe

65. CONFIG.SYS Commands Device
Allows us to install any hardware device that is supported by DOS.
Helps to install the device drivers in your computer’s memory.
Syntax:
device=<filename>
Example:
device=keyboard.sys

66. CONFIG.SYS Commands Files
Used to set and specify the number of files that can be opened simultaneously in DOS.
By default, the number of files are 8 and the maximum number that can be specified is 255.
Example:
Files=20

67. CONFIG.SYS Commands Last Drive
Used to tell how many drives are there in your computer.
By default, the last drive assumed to be E.
Syntax:
lastdrive=<drivename>
Example:
lastdrive=F

68. CONFIG.SYS Commands Shell DOS
DOS contains a file COMMAND.COM which is root directory of the hard disk. This command helps to specify another location for COMMAND.COM.
DOS
Used to load the operating system in the conventional, extended or reserved memory.

69. AUTOEXEC.BAT
A special batch file that is executed automatically when user boots the computer.
Executed after CONFIG.SYS file.
Can be used to set up the starting directory, change system prompt, change date/time or automatically start some program.

70. Setting the Environment

71. SET Displays, sets, or removes Windows environment variables. Syntax:
SET [variable=[string]]
variable
Specifies the environment-variable name.
string
Specifies a series of characters to assign to the variable.

73. Booting sequence

74. The BIOS loads the boot code in the master boot record and transfers control to it. The master boot record code begins execution.
The master boot code examines the master partition table. It is searching for two things.
It must determine if there is an extended DOS partition.
It must determine if there is a bootable partition specified in the partition table.

75. 3. If the master boot code finds an extended partition on the disk, it loads the extended partition table that describes the first logical volume in the extended partition. This extended partition table is examined to see if it points to another extended partition table. If it does, then that table contains information about the second logical volume in the extended partition, so it is loaded and examined. (Recall that logical volumes in the extended partition have their extended partition table chained one to the next.) This process is continued until all of the extended partitions have been loaded and recognized by the system.

76. 4. After loading the extended partition information (if any), the code attempts to boot the primary partition that is marked active (bootable). If there are no partitions marked active, then the boot process will terminate with an error. The error message is often the same one that occurs if the BIOS finds no boot device, and is generally something like "No boot device", but can be the infamous "NO ROM BASIC - SYSTEM HALTED".

77. 5.If there is a primary partition marked active, the code will boot it. The rest of the steps assume this is a DOS primary partition.
6. The volume boot sector is loaded into memory and tested, and the boot code that it contains is given control of the remainder of the boot process.

78. 7. The volume boot code examines the structures on the disk that it is booting to ensure that everything is correct and in the right place. If not, the boot process will end in an error here as well.
8. The code searches the root directory of the device being booted for the operating system files that contain the operating system. For a system running MS-DOS these are the files "IO.SYS", "MSDOS.SYS" and "COMMAND.COM".

79. 9. If the operating system files are not found, the boot program will display an error message, which is usually something like "Non-system disk or disk error - Replace and press any key when ready". Some people think that this message means the system was never booted, that the BIOS examined the floppy disk for example and just rejected it because it couldn't boot it. As you can see from this description of the boot process, the volume boot code was indeed loaded and executed, and in fact it is what prints the message when it can't find the operating system files!

80. 10. If the operating system files are found, the boot program will load them into memory and transfer control to them. First, IO.SYS is loaded and its code executed. IO.SYS will then executed MSDOS.SYS (in pure DOS systems--MSDOS.SYS is just a text file in Windows 95 and   later.) Then the more complete operating system code loads and initializes the rest of the operating system structures. For MS-DOS, this means loading the command interpreter (COMMAND.COM) and then reading and interpreting the contents of the CONFIG.SYS and AUTOEXEC.BAT system control files.