What is MS-DOS (Microsoft Disk Operating System)?

MS-DOS was a PC operating system created by Microsoft from QDOS and originally used by computers manufactured by IBM.

What is MS-DOS (Microsoft Disk Operating System)?

What is MS-DOS in Computer?

It is an acronym for an operating system created by Microsoft and installed by most computers. DOS, in addition to an operating system, is a set of programs that allow us to manipulate information on disks so that we can work with them easily, conveniently and quickly; Also, DOS coordinates the operation of the microprocessor so everything works fine inside our computer.

Microsoft has been developing DOS since its first release in 1981. Existing versions are used to correct errors detected in the previous version or to improve certain parts of the program. If the variation appears first, it means that significant changes have been made to the benefits of new microprocessors, for example, to take advantage of it to a large extent.


Perhaps it is an old and forgotten operating system by most users, but it forms the basis of the most current operating system.

It begins in 1981 with the acquisition of an operating system called QDOS, which is the first version of the Microsoft MS-DOS 1.0 operating system, after making a few changes.

A number of changes take place in the operating system until MS-DOS reaches version 7.1, where it ceases to exist and becomes an integrated part of the Windows operating system.


Among the versions or developments of the DOS operating system:

   PC DOS 1.0

PC DOS 1.0 is the first version of DOS released in 1981 in addition to IBM-PC. Supports 16 Kb RAM memory, 5.25 inch single-sided 160 Kb floppy disks. Allows files with .com and .exe extensions. It contains the COMMAND.COM command interpreter.

   PC DOS 1x

Many bugs fixed in PC DOS 1.1 version, support dual-density floppy disks. In 1982, version 1.25 was released, adding support for double-sided floppy disks.

With the version 2.0 that adds support for IBM 10 MB hard drives and the possibility to read 5.25 floppy disks with 360Kb capacity, it wasn’t until 1983 the next year, when the system had more functionality.

In the same year, new keyboard characters were added to version 2.11.

In 1984, Microsoft added support for 1.2 MB high-density disks in MS-DOS 3.0, and the possibility of installing a hard disk with a maximum of 32 MB. In the same year, support for MS networks was added in version 3.1.

Until 3 years later, in 1987, with the release of version 3.3 and the use of hard drives larger than 32 MB, it was allowed to support existing 3.3 and known 3.5″ floppy disks.

Microsoft released version 4.0 and with it XMS memory support and the possibility to include hard drives up to 2GB. It should be noted that this version is the biggest disaster carried out by the company, as it is full of failures. This was fixed in version 4.01, which corrected all these issues and errors in 1989.

One of the most relevant advances in MS-DOS history is the transition from version 4.01 to version 5.0 in 1991, where DOS can load programs into the high memory part of the system using higher memory. In version 5.0, the BASIC programmer and famous EDIT editor have been added.

A utility has also been added to run UNDELETE (Recovery of deleted files), FDISK (Partition Management) utilities, and SETVER programs designed for previous versions of MS-DOS. Some problems with UNDELETE and CHKDSK in version 5.0a were resolved at the end of 1992.

   MS-DOS 6.0

It appears with many new features that are responsible for compressing the disk and thus have more usable space, including a basic antivirus (MSAV), a defragmenter (DEFRAG), a memory manager (MEMMAKER) and some older features.

In the same year, version 6.2 was released in 1992, which adds security to the data loss of Doublespace and resolves issues with a new disk scanner, SCANDISK, DISKCOPY, and SmartDrive.

   MS-DOS 6.21

Appearing in 1993 in the same year, Microsoft is suppressing Doublespace and is looking for a new alternative for this utility.

A year later, the solution to the Doublespace problem in 1994, Stac Electronics, which chose to be included in version 6.22, appears to be the benefit of the Drivespace company.

   PC DOS 6.3

PC DOS 6.3 was released in April 1994. Already with the release of Microsoft Windows 95 in 1995, MS-DOS is taken to a secondary level.

However, the MS-DOS system is still a new version 7.0 in 1995, where many utilities have been fixed and provide support for long names. Utilities deleted from the previous operating system can be found in the Windows 95 CD\other\oldmsdos directory.

   MS-DOS 7.1

In 1997, Windows 95 OSR2 appears, and with it, a comprehensive revision of the DOS system adds support for FAT32 partitions, and this is the history of MS-DOS versions. It was later integrated into Windows 98 and 98 SE. Supports FAT32 file systems.

   MS-DOS 8.0

It is included in Windows Me. It is the latest version of MS-DOS.

   PC DOS 2000

It is the new version that solves the problem of the year 2000.

Currently, the MS-DOS operating system has very little use, in most cases, it is used only when Windows cannot perform its task or Windows fails. Many technicians in the computing area use MS-DOS to perform PC maintenance, setup, formatting, and partitioning of hard drives and scans.


MS-DOS is a single-user, single-task operating system for personal computers.

MS-DOS Commands

Here are some of the commands that MS-DOS uses and that are currently available from the command line on Windows operating systems:

CD directory_name: Hierarchically changes to the lower directory.
CD\ *PATH: Specifies the paths the operating system searches for executable files. It is usually a command written to Config.sys and batch files.
CLS: Clears all commands and all information on the screen, except for the letter of the drive used.
COPY: Copies a file from one directory to another directory.
COPY CON: Creates the .bat extension files.
DIR: Lists directories and files in the current drive or directory.
FOR: Repeats a command.
PROMPT: Changes the screen line of the directive.
MD: Creates a new directory.
RD/RMDIR: Deletes a directory.
REM: Adds comments to batch files.
REN/RENAME: Renames files and directories.
SET: Assigns values ​​to environment variables.
TIME: Displays or changes the time of the internal clock.
TYPE: Shows the contents of a file. It is often used to display file content in text format.
SEE: Shows the version of the operating system.
VOL: Shows the label and volume of the hard drive.
MEM: It shows the amount of RAM memory, the amount used, and free space.

External Commands

ATTRIB: Displays the attributes of directories and files without parameters. Replaces the attributes of directories and files with parameters.

The attributes of directories and files are: read (r), write (w), file (a), hidden (h), system (s).

Parameters: Attrib (plus or minus) and the letters r, w, a and h “v”. Example: Attrib + r *. * (Read-only attribute for all files in this directory)

APPEND: Used to specify paths for data files.
BACKUP: Backs up one or more files from the hard drive to a floppy disk.
CHKDSK: Checks for errors on the hard drive. (Can also be used to fix with “/F” parameter)
DELTREE: Deletes a directory without any subdirectories containing all of its directories.
DISKCOPY: It allows the creation of an identical copy from one floppy to another, it belongs to the group of external commands.
DOSKEY: It allows keeping commands executed at the indicator point built into RAM.
FC: Compares files.
FORMAT: Allows the creation of the logical structure on physical storage (hard drives, floppy disks, and mass storage units).
PRINT: It allows you to print files.

These parameters can be used together:

KEYB: Sets the keyboard language according to the added parameter.
LABEL: Shows or replaces the label of the hard disk drive.
MEM: Shows RAM, space used, and free space.
MOVE: Moves or changes the location of a directory or files. It also renames subdirectories.
SUBST: Creates a virtual logical drive from a directory.
TREE: Shows directories in tree format.


<: Redirection of the standard entry.

>: Redirection of the standard entry. If there is no file, it creates it and overwrites its content if any.

>>: Redirects standard output to an existing file. If there is no file, it creates, if any, adds the result of the command after the previous content of the file.

Control Mechanisms

MS-DOS is a single-user, single-task operating system. By meeting these two conditions, the processor is always specific to executing a process, so the planning of the processor is simple and dedicated to the only efficient process that can exist at any time.

MS-DOS includes five basic elements for controlling and deploying processes:

  1. ROM-BIOS.: It is an input and output management program between the Operating System and the basic devices of the computer.
  2. IO.SYS.: A series of instructions for transferring input/output from peripherals to memory. It initializes the system and includes built-in device drivers.
  3. MSDOS.SYS.: It is the MS-DOS kernel with instructions for checking diskettes. It is a program that manages files, directories, memory, and media.
  4. DBLSPACE.BIN.: It is the kernel controller of the hard disk compressor to increase the storage capacity of the disk, available from version 6 of MS-DOS. This drive performs all file compression and decompression operations and can be moved to higher memory than traditional memory.
  5. COMMAND.COM.: It is the interpreter of commands that the user communicates with the computer. It interprets the written commands and includes internal DOS commands that are not displayed in the system directory.

The IO.SYS, MSDOS.SYS and DBLSPACE.BIN files are hidden, meaning they do not appear when listing the directory and are loaded from disk to computer memory when starting the directory. In DOS control, there are 2 ways to boot the system:

  1. It caches input and output devices, keyboard, monitor, hard drives, floppy disks, memory (RAM). Then it looks at the floppy drive first and if there is a floppy disk with the operating system, it starts it. Otherwise, it looks at the hard drive.
  2. It is performed by turning off the computer with the reset button or Ctrl+Alt+Del. All previous tests are not done and are installed directly. It is usually used after the operating system crash or computer crash.

Among the programs that interfere with the control of the DOS operating system:


It is responsible for starting the computer. Also known as IPL (initial program load). Bootstrap program is programmed in the Basic program. The first program in the ROM is to read the startup program of the disk, which determines whether the IBMBIOS.COM and IBMDOS.COM files are on the disk.

If it finds the files, it first runs IBMBIOS.COM, which consists of two parts:

BIOS: It is the department responsible for the control of environmental units.
SYSINIT: It is responsible for determining the amount of continuous memory in the computer.

It then runs IBMDOS.COM and SYSINIT goes from the low part of the computer memory to the high part and leaves the low part to IBMDOS; The first thing it does is a control that peripherals work properly. After controlling peripherals, SYSINIT returns and calls Kernel services and executes the CONFIG.SYS file.

Finally, SYSINIT calls DOS services and installs COMMAND.COM. The launch part will load the AUTOEXEC.BAT file.

After that, the startup partition SYSINIT and COMMAND.COM are cleared from memory.


Refers to the Basic Input/Output System. It is specific to each manufacturer and is responsible for controlling the input and output hardware units. The BIOS is loaded by reading the IBMBIOS.COM or IO.SYS file and saved in RAM.


It is the core or core of the system. Its functions are file management, memory management, creation of other programs. It is independent of the hardware used. It includes a number of services.


It is an interface between the user and the device through a series of prompts and response messages for user commands. He is responsible for grammatical analysis and manages the user’s commands.

COMMAND.COM is also responsible for managing interruptions; The cutting system has a simple priorities hierarchy to deal with interruptions caused by peripherals. When an interruption treatment ends, the control is returned to the running program when the interruption occurs.

It is also about addressing any error that may occur during the execution of a program, returning control to the program where the error occurred, and, if possible, MSDOS.

It manages the internal commands directly linked to it. It is not mandatory to use it.

It is divided into three parts:

  1. Settled: It is installed under the memory, on top of the kernel and BIOS. Ctrl + Break processes critical errors using Ctrl + C keys.
  2. Initialization partition: It is loaded on top of the built-in partition and is responsible for the processing of the AUTOEXEC.BAT file, then it is deleted from the RAM memory.
  3. Temporary module: It is loaded into the upper part of the memory and its purpose is to prepare the command prompt or command prompt required to enter and execute instructions. It is installed only when needed and removed after the command is executed.


Config.sys is a system file created or modified with any text editor.

It runs before Autoexec.bat and includes a set of computer configuration commands. Some of its parameters show the number of files that can be opened simultaneously. It has no size limitation and should be located in the root of the disk. In addition to the files, there are other “typical” commands in this file:

  • Buffers: It is the intermediate storage area where things are temporarily stored to transfer data.
  • Country: Indicates the country you are working in so that the correct characters of the country are displayed.
  • Device: Used to install mouse, keyboard, and other features.
  • Break: It tells DOS whether to check by pressing Ctrl + C or Ctrl + Break.
  • Lastdrive: Specifies the last letter of the disk drive that the system will recognize.


This is a batch file. It is used to start a series of non-essential functions, enter data, activate system controls, and automatically load programs.

If there is an operating system, it runs automatically. It has no size limitation and should be in the directory where the system is booting. There are usually a few commands included:

  • Keybsp: Updates the keyboard.
  • Path: Searches for a program in any folder specified in this command.
  • Set: It contains environment variables and their corresponding values.

Like any batch file, AUTOEXEC.BAT has the same features as others: it has a BAT extension, contains commands, can be run by entering its name after the command prompt, and if we press Ctrl + Pause, the process is interrupted. In addition, three special features have been added:

  • It has a mandatory name and extension: it should always be called AUTOEXEC.BAT.
  • The computer runs every time it starts up. Otherwise, It runs three commands instead: Date, Time, and Ver.
  • It should be located in the root directory of the boot drive.

The AUTOEXEC.BAT file also contains commands to configure the user’s language.

Therefore, the following three basic modules should be included in the AUTOEXEC.BAT file:

  • Configuring environment variables.
  • Instructions to choose the language.
  • Orders for installing built-in programs.

The first set of commands contains the definition of environment variables. Note that PATH and PROMPT variables can be defined by the Set command or by specially designed commands called Path and Prompt.

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