What is the DOS file format?
Files with the .DOS extension were used on Microsoft operating systems in the 1990s - MS Windows 95 and MS-DOS 7. .DOS files were created on the disk when two operating systems were installed on the same computer: MS-DOS and then Windows 95. In order to have the option to run either system, a dual-boot configuration was required.
To prevent mix-ups between the two sets of system files, DOS system files such as AUTOEXEC.BAT (a .BAT batch file) or CONFIG.SYS had their extensions changed to AUTOEXEC.DOS and CONFIG.DOS, respectively. The COMMAND.COM file was similarly renamed to COMMAND.DOS. Adding the .DOS extension to these files did not change their contents - the format of each file remained identical to the original.
At startup, pressing F4 (or setting BootMulti=1 in MSDOS.SYS) would instruct the Windows 95 boot process to load the old MS-DOS environment using the .DOS files instead of the Windows 95 versions.
This usage of the .DOS extension is no longer common. MS-DOS and early MS Windows systems are considered legacy software and are no longer developed or maintained, as are their system files. Modern dual-boot setups are handled by the Windows Boot Manager (BOOTMGR) and standard bootloader configuration; the .DOS renaming mechanism is specific to Windows 95 and Windows 98 and has no equivalent in Windows NT, 2000, XP, or any later version.
Security & safety
RISK: LOWDOS files are historical system files from Windows 95/98; they pose no risk on modern systems as they are not executed by current Windows versions. They may contain path references or commands obsolete on modern hardware.
Format details
in a nutshellPrograms that open DOS files
Windows2 apps
DOSBox
Open-source Use DOSBox to emulate a DOS environment where these system files are active (place them in the emulated C: drive). 
Notepad
Built-in Right-click → Open with → Notepad. Most .dos files are plain-text batch or config files. 
macOS1 app
Linux1 app
Any text editor (gedit, nano, vim)
Open-source Open in any text editor; .dos files are plain ASCII text (for batch/config renames). Technical details
deep spec| File encoding | Inherits the encoding of the original file: ASCII text for .BAT and .SYS renames; binary for .COM renames |
| Container | None - a .dos file is a renamed copy of an existing MS-DOS system file; no new format is applied |
| Magic bytes | None fixed - byte signature matches the original source file type |
| Typical file size | Under 10 KB - MS-DOS system configuration files are small |
| Associated OS | MS-DOS, Windows 95, Windows 98; absent from Windows NT and all subsequent Windows versions |
| Dual-boot activation | Press F4 at startup, or set BootMulti=1 in MSDOS.SYS, to boot old MS-DOS using the .dos renamed files |
| Common renamed files | AUTOEXEC.DOS (from AUTOEXEC.BAT), CONFIG.DOS (from CONFIG.SYS), COMMAND.DOS (from COMMAND.COM) |
| Created by | Windows 95 setup installer, automatically during installation over an existing MS-DOS system |
| Dual-boot scope | Exclusive to Windows 95 and Windows 98 dual-boot installations; Windows NT, 2000, XP, and later do not use this mechanism |
| Current status | Obsolete - modern dual-boot is handled by Windows Boot Manager (BOOTMGR) and bootloader configuration files |
| Released | 1995 (Windows 95) |
DOS conversions
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