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MS-DOS Operating System

A disk operating system (DOS) is an operating system for x86 based personal computers mostly developed by Microsoft. MS-DOS, its rebranding as IBM PC DOS, and some operating systems attempting to be compatible with MS-DOS. Sometimes it is referred to as "DOS", which is also the generic acronym for disk operating system.

MS-DOS was the main operating system for IBM PC compatible personal computers during the 1980s. It was gradually superseded by operating systems offering a graphical user interface (GUI) in various graphical Microsoft Windows operating system generations.

DOS is also used to describe several similar command-line disk operating systems. Early computers, such as the Commodore 64, Atari 800, and Apple II, all featured a disk operating system, including Commodore Business Machines DOS, Atari DOS, and Apple DOS, respectively. DOS/360 was an OS for IBM mainframes, which first appeared in 1966, but it is unrelated to the 8086-based DOS of the 1980s.

MS-DOS Operating System

Several competing products were released for the x86 platform during its lifetime, and MS-DOS went through eight versions until development ceased in 2000. Initially, MS-DOS was targeted at Intel 8086 processors running on computer hardware using floppy disks to store and access the operating system, application software, and user data.

Progressive version releases delivered support for other mass storage media in ever greater sizes and formats and added feature support for newer processors and rapidly evolving computer architectures. Microsoft's development was the key product from a programming language company to a diverse software development firm, providing essential revenue and marketing resources. It was also the underlying basic operating system on which early versions of Windows ran as a GUI.

How DOS works?

When a computer is powered on, it goes through various steps called the boot process. For a computer running a disk operating system in the following six steps, such as:

  1. The read-only memory (ROM) bootstrap loader reads the Master Boot Record and passes control over to it.
  2. The boot record loads the disk operating system into memory, and it takes control of the machine.
  3. The computer transfers data stored on a magnetic disk to its main memory, the random access memory.
  4. It also transfers data to external devices attached to the computer, such as a computer screen or printer.
  5. The computer provides various applications programming interfaces for programs like character input/output, memory management, program loading, termination, and handling input from the user through a keyboard.
  6. The OS also provides file management that organizes, reads, and writes files on storage. The files are organized in a hierarchical structure of directories, subdirectories, and files.

A disk operating system doesn't have a graphical user interface (GUI). Its interface is character-based, so users must type commands in the command line to indicate what actions they want.

Features of DOS

Here are some of the distinguishing features of a disk operating system, such as:

  • MS-DOS does not offer GUI (Graphical User Interface) and doesn't accept mouse inputs. It is a character-based interface system where all commands are entered in the text at the command-line prompt.
  • A disk operating system manages files, folders and allows program loading and execution. It can control hardware devices such as disk, memory and allocate resources.
  • MS-DOS offers a file system to organize, read and write files to the disk storage.
  • It is a single-user operating system and performs various tasks to ensure the proper operation of systems.
  • It uses a 16-bit file allocation table (FAT16), and a 16-bit interface is used to define the location of the memory of each file uniquely. These identifiers are stored in a tabular format with the name File Allocation table.
  • MS-DOS does not support a multiuser operating system, and it is less secure and does not have a concept of user roles. It is very lightweight due to its basic interface and limited features.

Limitations of MS-DOS

Here are the following limitations of the disk operating system, such as:

  • Built-in security:DOS does not have built-in security, such as file ownership and permissions.
  • No multiuser or multitasking:It also does not support multiuser or multitasking. It can only run one program at a time, but it provides direct access to the basic I/O system and underlying hardware.
  • Challenging interface: A user must type in commands and remember commands to run programs and other OS tasks. For example, typing the command cd \directory_name changes the current working directory to the named directory, and typing the command dir lists the files in the current directory. This approach makes it difficult for beginners to use.

Types of MS-DOS Commands

An instruction given to a computer to perform a specific task is known as a command. The MS-DOS has many commands to perform each task, and these commands are stored in the DOS directory of the disk. The MS-DOS commands are of two types, internal command, and external command.

  1. Internal Command: Internal commands are built-in commands of MS-DOS, stored in the command interpreter file (COMMAND.COM). These commands reside in memory if the system is at prompt (C:\>) level. Some of the internal commands are DATE, TIME, DIR, VER, etc.
  2. External Command: External commands are separate program (.com) files that reside in the DOS directory.

MS-DOS is not case-sensitive so that commands can type in either uppercase or lowercase. However, other disk operating systems have case-sensitive CLIs. DOS commands include the following.

Commands Description
Dir List all files of specific directories or subdirectories.
CD or CHDIR Navigate or move to a specific directory.
RD or RMDIR Remove directory.
TREE Display all directory paths.
PATH Set sequential search path for executable files.
SUBST Substitutes a string alias for the pathname.
FORMAT Formats a disk for DOS files.
COPY Copies one or more files to another location.
XCOPY Copy files and directories and their subdirectories.
Del Delete files.
Ren or rename Rename the name of a file or directory.
ATTRIB Set or show file attributes.
BACKUP Backup files and directories.
PROMPT Customize DOS prompt.
Deltree Deletes all files and subdirectories from a computer.
Help Lists the available commands or more information about a specific command.
mkdir or md Creates a new subdirectory.
Move Moves files or directories from one directory to another or from one drive to another.
Type Displays the contents of a file on the screen.
* A wildcard character that represents one or more characters a group of files has in common.
? A wildcard character that represents a single character a group of files has in common.

MS-DOS Files and Filenames

One of the primary functions of the OS is to handle disk files. A file can contain only data, or it can contain a set of instructions, called a program, telling the computer how to perform a particular task. Every file has associated with it a unique filename which is used to identify it on the disk. A filename in MS-DOS has two parts; the name and an extension.

The name can contain up to eight characters. Each filename can have a three-character extension. The extension is separated from the name by a period. The period serves as a delimiter, indicating where one portion of the filename ends, and the next begins. An extension is usually used to identify files that are related in some way. MS-DOS allows the following characters to be used in a filename and extension:

  • Uppercase and lowercase case letters A through Z
  • Numbers 0 through 9
  • Special characters $ # & @ ( ) ! ^ ` ~ { }

Any other character used in a filename, including spaces, will cause the name to be terminated at that character. It is generally good practice not to use special characters in filenames because some programs may use them as delimiters or other special purposes.

In addition, the extensions BAT, COM, EXE, and SYS have special meanings in MS-DOS and should therefore normally not be used with your data files. Shown below are examples of both valid and unacceptable filenames.

Valid MS-DOS Filenames:

  • DAT
  • 1
  • EXP

Invalid MS-DOS Filenames:

  • EXP 1.DAT (space is not allowed)
  • BEERSLAWDATA (too many characters in the name)
  • EXP1 (too many characters in the extension)
  • HG>HE (> is an invalid character)

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