What is the DEV file format?
The .dev extension has several distinct uses. Its most historically significant role is as a real-mode MS-DOS device driver binary, loaded at system boot via a DEVICE= or DEVICEHIGH= directive in CONFIG.SYS.
In this context, a .dev file is a binary executable whose first 22 bytes form the DOS device driver header: a next-driver link pointer (set to 0xFFFF:0xFFFF for the final driver in the chain), an attribute word encoding device type and capabilities, strategy and interrupt routine offsets, and an 8-character device name. The body contains x86 real-mode code implementing the Strategy and Interrupt routines the DOS kernel calls to communicate with the hardware.
This format originated with MS-DOS 2.0 (1983), which introduced installable device drivers. While DOS drivers more commonly used the .sys extension, certain hardware vendors - particularly SCSI and sound card manufacturers - used .dev. The format became obsolete with Windows NT, which replaced real-mode drivers with kernel-mode .sys and WDM .drv drivers.
The .dev extension also identifies two unrelated formats: Embarcadero Dev-C++ uses it for C/C++ IDE project files stored as plain-text INI data; Parallels Desktop (macOS) uses .dev for virtual machine device descriptor files. These formats share only the extension and have no connection to DOS drivers.
Security & safety
RISK: MEDIUMGenuine DOS .dev drivers contain executable x86 real-mode machine code. On modern Windows they cannot auto-execute (no CONFIG.SYS mechanism). However, malware could theoretically use the extension to disguise itself. Dev-C++ .dev project files are plain text and safe to open. Do not attempt to run unknown .dev files.
Format details
in a nutshellFULL NAMEDOS/Windows Device Driver Fileaka Device Driver, DOS device driver
DEVELOPERN/A (OS-level format; originally MS-DOS, extended by Microsoft for Windows)since MS-DOS 2.0, 1983 (loadable device drivers via CONFIG.SYS)
CATEGORYSystem Files
MIME TYPEapplication/octet-stream
TYPEbinary executable (DOS device driver)
This extension is also used by…
- Dev-C++ Project File - Embarcadero Dev-C++ (Windows C/C++ IDE) uses .dev for project files - XML/text format, unrelated to drivers.
- Parallels Desktop device descriptor - Parallels Desktop for macOS uses .dev internally for virtual hardware device configuration.
MAGIC BYTES · FILE SIGNATURE
OFFSET
0001
HEX
FFFF
ASCII
··
DOS device driver header begins with 0xFFFF 0xFFFF (next-device pointer = end-of-chain marker). Followed by WORD attribute flags, WORD strategy routine offset, WORD interrupt routine offset, 8-byte device name. No universal magic; the 0xFFFF sentinel is conventional but not enforced by all implementations.
Programs that open DEV files
Windows3 apps
Microsoft Windows (system loader)
Paid DOS .dev drivers load only in MS-DOS or Windows 9x via CONFIG.SYS DEVICE= line - not openable in modern Windows. View in a hex editor only.
Embarcadero Dev-C++ (if it is a Dev-C++ project file)
Free File → Open Project → select the .dev file. 
macOS1 app
Parallels Desktop
Paid Parallels uses .dev files internally; accessed only by Parallels - not user-opened. Technical details
deep spec| Primary use | MS-DOS installable device driver binary (loaded via `DEVICE=` in `CONFIG.SYS` at boot) |
| Encoding | Binary - x86 real-mode executable code |
| Byte order | Little-endian (x86) |
| Driver header | 22-byte structure: next-driver pointer (4 bytes, `0xFFFF:0xFFFF` for last driver), attribute word (2 bytes), strategy and interrupt routine offsets (2 bytes each), 8-char device name |
| End-of-chain marker | `0xFFFF:0xFFFF` in the next-driver pointer field |
| Execution environment | x86 real mode - MS-DOS, Windows 3.x, Windows 95/98/ME (DOS mode only) |
| Load directive | `DEVICE=` or `DEVICEHIGH=` in `CONFIG.SYS` |
| Typical file size | 1 KB - 64 KB (DOS-era drivers are compact) |
| Superseded by | `.sys` kernel-mode drivers (Windows NT/XP+) and WDM `.drv` drivers |
| Alternate use 1 | Dev-C++ IDE project file (Embarcadero Dev-C++): plain-text INI format, unrelated to DOS drivers |
| Alternate use 2 | Parallels Desktop (macOS): virtual machine device descriptor file, unrelated to DOS drivers |
| Released | MS-DOS 2.0, 1983 (loadable device drivers via CONFIG.SYS) |
| Latest version | N/A - legacy DOS-era format; superseded by .sys/.drv in Windows |
DEV conversions
Community Q&A
asked by users
Q
Frequently asked questions
What is a .dev file on Windows?
It is most likely either a legacy DOS device driver (real-mode binary from the MS-DOS era) or a Dev-C++ C/C++ project file. On modern Windows you will rarely encounter genuine DOS drivers.
Can I open a .dev file?
If it is a Dev-C++ project file, open it with Embarcadero Dev-C++. If it is a DOS driver binary, use a hex editor to inspect it - you cannot run it on modern Windows.
Why does my antivirus flag a .dev file?
DOS driver files contain real-mode x86 executable code, which some heuristic scanners flag. A genuine legacy driver from a known software package is not malware, but treat unknown .dev files with caution.
Is .dev related to .drv or .sys drivers?
.sys is the modern Windows kernel-mode driver extension (NT family). .drv is for Windows user-mode drivers. .dev was a DOS-era convention and is not a standard Windows extension.
References
1MS-DOS Installable Device Drivers - Microsoft Docslearn.microsoft.com
2DOS device driver - Just Solve the File Format Problemjustsolve.archiveteam.org
