1.2.1 DOS Operating System

MS-DOS (Microsoft Disk Operating System) was originally developed by Microsoft for IBM, MS-DOS was the standard operating system for IBM-compatible personal computers.

Though UNIX was a powerful operating system available, but it was not suitable for 8-bit 8086 microprocessor based Personal Computers. So there was a need for a small operating system that could work in 640K memory(RAM).

DOS was an variant of CP/M (Control Program/Monitor) which ran for the first time on IBM-PC in 1981. It is called so because it resides on Floppy or Hard disk and provides command level interface between user and the computer hardware.

The different versions of MS-DOS have evolved over a period of time with Microsoft introducing new features in each new releases. Starting with MS-DOS1.1, the latest version was MS-DOS6.22 released in 1994. There are various versions of DOS like MS-DOS(Microsoft), PC-DOS(IBM), Apple DOS, Dr-DOS etc.

 

DOS Files

—  The main portions of MS-DOS are the IO.SYS, MSDOS.SYS, and COMMAND.COM files.

—  IO.SYS and MSDOS.SYS are special, hidden system files.

—  The IO.SYS file moves the system’s basic I/O functions into memory and then implements the MS-DOS default control programs, referred to as device drivers, for various hardware components.

—  The COMMAND.COM command interpreter accepts commands issued through the keyboard, or other input device, and carries them out according to the commands definition.

—  When DOS runs an application, COMMAND.COM finds the program, loads it into memory, and then gives it control of the system. When the program is shut down, it passes control back to the command interpreter.

Types of DOS commands

Any instruction given to the computer to perform a specific task is called command.

The DOS has several commands, each for a particular task and these are stored in DOS directory on the disk. The commands are of two types:

(a)Internal Commands: These are in built commands of MS-DOS i.e. these are stored in Command interpreter file (COMMAND.COM). These commands reside in the memory as long as the machine is at the system prompt(C:\>) level. To use these commands no extra /external file is required. E.g. DATE, TIME, DIR, VER etc.

(b) External Commands: These are separate program (.com) files that reside in DOS directory and when executed behave like commands. An external command has predefined syntax. for e.g. HELP, DOSKEY, BACKUP, RESTORE, FORMAT etc.

 Internal DOS Commands

—  dir (Directory) - used for listing files and directories present in the current disk.

—  cd (Change Directory) - We can enter or exit from any directory using this command.

—  md (Make Directory) - This command allows to create a new directory.

—  rd (Remove Directory) – This command is used to remove a directory from the disk.

—  ren (Rename) - This command is used to change the name of any file or directory.

—  del (Delete) - This command is used for erasing any file from the disk.

—  type - This command is used to display the contents or text of any file to the display device.

—  date -  Display the current Date

—  time - Display the current Time

—  cls (Clear the Screen) - This command is used to clear the screen or wipe out everything written on the screen.



External DOS Commands

—  attrib  - This command is used for protecting the files from accidental changes or modification. used for listing files and directories present in the current disk.

—  chkdsk - This command checks the status of the disk; it shows a graphical display, information about the user file. 

—  tree – This command graphically displays the path of each directory and sub directory in given drive.

—  edit  – This command loads the MSDOS editor, where we can edit files, create new files, open existing files.

—  sort - This command is used for sorting data and displaying the result on the screen.

—  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.

—  sys - This command transfers MSDOS System files to specified areas to make the disk bootable.

—  echo -  This command can be used to display a message on the screen.

—  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”.

—  doskey - Once we install doskey, our dos will star to memorize all commands we use. We can recall those commands using up or down arrow keys. It also gives the facility to create macros, which creates a short key for long keyword or command.