DOS OPERATION

A disk operating system (abbreviated DOS) is a computer operating system that can use a disk storage device, such as a floppy disk, hard disk drive, or optical disc. A disk operating system must provide a file system for organizing, reading, and writing files on the storage disk. Strictly speaking, this definition does not apply to current generations operating systems, such as versions of Microsoft Windows in use, while this definition is actually only used for older generations of operating systems.

Disk Operating System: (Internal/External)Commands

When a Computer is switched on POST (Power on Self Test) operation is performed, which checks integrity of all components (CPU, Memory, I/O devices) of the system. If a component is found faulty , error message will be displayed. A chip called ROM - BIOS is read and executed. BIOS (Basic Input Output Services) information is a pre-written program that is permanently stored on ROM chip. DOS commands are generally classifieds in two types.

Internal Command

DOS commands for which the specifications are available in Shell (Command.com) are calledinternal commands. These are frequently used commands, and are called resident commands.

DOS Commands for which specifications are not internally available in command.com are called External Commands. They reside in the disk in the form of executable program files. They will be loaded into primary memory only at the time of execution.

Directory Structure of DOS: One thing is to be kept in mind is that a directory can have as many child (sub) directories, but the child directory can have only one parent directory.

1. CLS: this command is used to clean the screen.

2. DIR: this command allows the user to see all files and sub-directory in the current directory. DIR Command lists file information in five columns; (first) column gives primary name of the file (second) column gives extension of the file (third) column gives the file size - number of bytes used; (fourth) column gives the last updated date; (fifth) column gives the last updated time.

Dir/p - page by page display of file name and directory names;

Dir/w - width-wise display;

Dir/s - displays all sub directory and files in the sub-directory of current directory.

3. Copy con this command copies whatever typed on keyboard to the file; the file can be closed by giving the command A2 or F6 key: eg: Copy con test .....A2.

4. Date it displays two system date and allows the user to change it if desired ; it is displayed in the form of mm - dd - yy; eg:c:\> date - enter.

5. Time it displays the system type and enables the user to change it; eg: C:\> Time - enter.

6. md(mkdir) it creates a new directory in sub directory in the current directory; eg: C:\> md <New directory name>

7. rd(rmdir) this command is used to remove a directory from the disk; it can't remove a directory which contains sub directory or files, ie, the child should be removed from the parent; similarly this command can't remove the current directory and root directory. Syntax: c:\> RD<Dir name>.

8. Type it displays the content of saved file; eg: C:\> Type> file name.

9. Ren this command changes the name of existing file or directory: Syntax: C:\> ren <old name> new name>

10. Delete delete a file from current directory; Syntax: C;\> del<file name>

11. Ver it displays the version of DOS currently being used in the system; Syntax: C:> ver

12. Copy it copies the given file or files from the source directory to the largest directory; Syntax:C:\> copy<source file name> <target file name>.

13. Prompt allows the user to set a new DOS prompt instead of usual C:\> or A:\>; eg C:\> prompt pcc; Prompt$p$g - this allows you to reset default prompt; Prompt $d (current date); Prompt $t (current time);

External Command

1. Attrib this command is used for protecting the files from accidental changes or modification. It can also be used for making a hidden file, archive files, read only files; Syntax: Attrib +R/-R/+H/-H/+A/-A <file name> +FR protects the file by making it read only, -R removes the read only protection; eg: Attrib + r <file name >

2. Scandisk/ Chkdisk this command checks the status of the disk; it shows a graphical display, information about the user file.

3. Tree this command graphically displays the path of each directory and sub directory in given drive; Syntax: C:\> tree<

4. More it displays one screen of data at a time and is used with another command when one screen is full; if you press any key on the next screen is displayed: Syntax C:\> type abc.doc| more.

5. Edit the command loads the MSDOS editor, where we can edit files, create new files, open existing files; Syntax: C:\> edit < file name>

6. Label a label is a name given to a disk which refers to collection of filers and directories on disk; Syntax: C:\>label A.

7. Sort this command is used for sorting data and displaying the result on the screen: Syntax:C:\>dir/sort/r (reverse order)

8. Format; this command prepares a disk by arranging random magnetic impulses in to a series of track and sectors so that it is addressable by a DOS version; Syntax : C:\> format A:/s

9. Sys this command transfers MSDOS System files to specified areas to make the disk boo table; Syntax: C:\>Sys A:<

10 Pipes (|) it connects two files ie the standard output of one filter command becomes standard input of another filter; eg Dir/Sort/ more ||

11. Batchfiles all batch files on DOS must have the file extn on bat to execute the batch file, the user has just type the file name and press enter key, in addition to usual DOS command.

12. Echo this command can be used to display a message on the screen

13. Pause when this command is obeyed, the system waits for the user to press a key by displaying a line "strike a key when ready"

14. Rem a command or remark can be used on batch file by the rem command; to symbol @ can be put in a REM command to prevent DOS from displaying the commend during the execution of batch files.

Config.Sys the purpose of this file is to tell DOS how to configure the computer; it contains configurable parameters of DOS, such as number of drives, files, buffers that can be opened at a time.

break - ON/OFF it can be used to change the frequency to check the break character (Ctrl+c, ctrl+break); it break + OFF, then the frequency of checking is less, otherwise it is ON, then it makes DOS extensively check the break character.

Buffer = 20/10 it tells DOS how many disk buffers be maintained; the default value is 2 each buffers of 528 bytes (512 + 16); this feature is needed for file manipulation, because the performance increase with the addition of buffers.

Device: Ansi.Sys/V Disk.Sys/Tapeover it tells DOS how to include a particular device driver which controls and configure a device such as Floppy disl or Tape Unit.

Files = 10/20/30 it tells DOS how many files to be opened at one time, its default value is 8; a max of 99 files can be opened at a time

Stacks = 15, 128it tells DOS the number of stacks to be used by the H/W interrupts; the default value is 9 with 128 byte.

Shell = Command.com it tells DOS to install the command processor from a particular path such as Shell = C:\DOS\ Command.com