DOS

N.B Red colour indicates that the command is dangerous to use or generally not used.

DOS is a single tasking operating system

• COMPONENTS OF DOS:

There are four components of MS DOS, viz.

1. The bootstrap program: When the computer is switched on the ROM (read only memory), loads the bootstrap routine into the memory and execute it. The bootstrap program takes over from this point and its function is to load the other files in MS DOS.
2. The basic input output system: This program is loaded into the memory by the bootstrap loader. This is the interface between the hardware and software of the system. The file system is IO.SYS or IBOBIM.COM.
3. The file and disk manager: This contains the file management capability. The file name is MSDOS.SYS or IBMDOS.COM. 
4. The command processor: This interprets the command given by the user. File name --> Command.com.

• DOS COMMANDS :

DOS commands can be catagorized in two parts,

1. Internal Commands : There are some commands that can be executed at system prompt without the help of the external storage source. In other words, these commands are clipped togather into a file command.com. The file is loaded into the memory along with DOS and remains in the memory till the machine is switched off. Thus the commands which form the part of Command.com are called internal command.
2. External Commands: These commands are also executed at system prompt but requires the aid of an external source of files or commands. The commands which don't form the part of Command.com are called external commands. External commands can be executed only if they are present in the disk or floppy, otherwise the user will get an error message. These files have to have an extension of .COM or .EXE (executable file), .BAT.

• SOME IMPORTANT INTERNAL COMMANDS :

1. A:  Change default drive to A-drive.
2. CD: Change directory.
3. CD.. : Goto parent directory from subdirectory.
4. CD\ : Go to root directory from any subdirectory.
5. CLS : Clear Screen.
6. COPY : Copy any file or directory from one location to another. (e.g. COPY source destination)
7. DATE : Display and update system date.
8. DEL : Delete file (To get confirmation i.e. Y/N option for delete, use DEL/P filename)
9. DIR : Display directory listing of current drive of an secondary storage media (e.g. floppy or hard disk. etc).
10. DIR/P : Directory listing pagewise.
11. DIR/W : Directory listing widthwise.
12. DIR/O : Directory listing in alphabetical order.
13. DIR/B : Displays filename without any other related information (Like, size, time, date of storage etc.)
14. DIR/S : Lists contents of subdirectories under current directory.
15. DIR/A followed by attributes : displays files only which satisfy the mentioned attribute. The attributes are, S= System files, R= Read onlyfiles, D= Directories, H= Hiddenfiles.
16. ATTRIB followed by + or - followed by attribute type (S, R, H) followed by filename : Set the particular attribute to the file.
17. PATH : Displays the path of executable files.
18. PROMPT : To change system prompt (Default prompt $P , $G).
19. RD : Remove directory.
20. REN : Rename any file or directory. (e.g. old filename REN new filename).
21. TIME : Displaying or updating system time.
22. TYPE : Display the content of any file.
23. VER : Display version of operating system.
24. COMMAND NAME / : Helps to display the switches of the present command.

• SOME IMPORTANT EXTERNAL COMMANDS :

1. CHKDSK : Check the integrety of the disk.
2. DEFRAG : DOS is often forced to fragment files to fit them in the available space on the disk. Fragmentation doesnot affect a file but the speed of access of file decreases.
3. DELTREE : Deletes a whole directory with all of its subdirectories and all files present in a particular subdirectory at a time.
4. DISKCOPY : Makes a complete copy of another diskette, sector by sector.
5. DOSKEY : This command helps in recording DOS keyboard commands, so we can recall it when necessary and then run it again. This is a TSR (Terminate and stay resident e.g. virus program) program. (It is a reusability feature).
6. EDIT : Create and alter text files.
7. FORMAT : Erases the existing files in a disk and devides it into section for fresh storage of files.
8. MOVE : Moves one or more files to the location specified. (e.g. MOVE source destination)
9. SYS : Transfer system files from one disk to another.
10. XCOPY : Copy one or more files or one subdirectory to another. Executes faster than COPY command.

• SOME MORE COMMANDS :

1. MD Directory name : create or make directory.
2. COPY CON : Copy from console (input device e.g. keyboard).

• BATCH FILES : Special type of file, used for performing a set of tasks again and again. Extension .BAT
• SYSTEM FILES : Basic inbuilt files, required to run an operating system.
• SOME IMPORTANT KEYS :

1. F7 : Displays list of commands recorded by the DOS programme.
2. F9 : To get the line number.