What is the SET file format?
The .set extension identifies Microsoft Backup File Set files - catalog definitions written by MSBACKUP and MWBACKUP, the backup utilities bundled with MS-DOS 6 and Windows 9x. Rather than containing backed-up data, a .set file holds information regarding which files belong to a backup job, acting as a manifest for the set. Actual backup data is stored separately, typically in a .QIC or .BAK archive.
Functioning of .set files
.set files should not be opened manually, because the application loads them automatically when resuming or restoring a backup job, so that the previously stored job configuration is visible from its start. Manual opening and modifying a .set file may result in malfunctioning of the backup process. Because many unrelated programs also use .set for configuration or settings, a file cannot be reliably identified by extension alone - its meaning depends on the application that created it. The original MSBACKUP tools are now obsolete; Windows XP replaced them with NTBackup, which produces .BKF files.
Security & safety
RISK: LOWA .set is data (a settings or backup-definition file), not an executable, so it won't run by itself. Risk is mostly breakage: editing or deleting a program's .set can reset or corrupt that program's options - back it up first. Legacy Microsoft Backup .set files are inert. As always, only open an unknown .set in a viewer/text editor, not by guessing an associated program, until you know what created it.
Format details
in a nutshellFULL NAMEMicrosoft Backup File Set
DEVELOPERMicrosoftsince MS-DOS 6 / Windows 9x era Microsoft Backup (MSBACKUP / MWBACKUP), early-to-mid 1990s
CATEGORYBackup Files
MIME TYPEapplication/octet-stream
TYPEBackup set definition / catalog written by Microsoft Backup (msbackup)
This extension is also used by…
- Generic program settings (SET) - Many apps (AutoCAD, Corel Painter, Nikon Capture/Capture NX, GTA and others) save preferences/options in a .set file inside their install or profile folder.
- EEGLAB dataset (.set) - MATLAB's EEGLAB toolbox stores an EEG dataset as a .set file (paired with a .fdt data file) - common in neuroscience research.
- Sibelius sound set - Sibelius music-notation software uses .set files to define instrument/playback sound sets.
Programs that open SET files
Windows3 apps
Original application that created it
Built-in Identify the program (by folder/origin) and let it load its own .set; e.g. AutoCAD/Painter read their .set settings automatically - don't open it by hand.
Microsoft Backup (legacy)
Built-in MS-DOS/Win9x case: the matching Microsoft Backup version loaded the .set to re-run/restore a backup job. No modern Windows tool reads these.
Notepad++ / hex editor
Open-source Inspect an unknown .set: open in a text/hex editor to see whether it's readable settings or binary, to help identify its source program. 
macOS1 app
Original application that created it
Built-in Determine the source app and let it use the .set; for inspection open in a text editor if it's plain text. 
Linux1 app
EEGLAB (MATLAB/Octave)
Open-source Research case: load an EEGLAB .set dataset with pop_loadset (needs the paired .fdt data file). Technical details
deep spec| File role | Backup job definition and catalog - records which files belong to a backup set, not the backed-up data itself |
| Developer | Microsoft |
| Created by | MSBACKUP (MS-DOS 6) and MWBACKUP (Windows for Workgroups / Windows 9x) |
| Era | Early to mid 1990s - MS-DOS 6 through Windows Me |
| MIME type | application/octet-stream |
| Encoding | Binary - proprietary internal structure, not human-readable plain text |
| File signature | None - no stable public magic bytes; cannot be identified by file header alone |
| Extension ambiguity | Many unrelated applications independently use .set for settings or preferences; meaning is wholly application-specific |
| Companion file types | .QIC (backed-up tape data archives), .BAK (generic backup data) |
| Successor format | NTBackup .BKF files (Windows XP and later) |
| Operating systems | MS-DOS 6, Windows 3.x, Windows 95, Windows 98, Windows Me |
| Obsolescence | MSBACKUP and MWBACKUP were discontinued; no current backup software reads these catalogs natively |
| Job metadata stored | File selection sets, backup type (full or incremental), destination path and schedule options |
| Identification method | Context only - must be determined by the creating application rather than file signature or extension |
| Released | MS-DOS 6 / Windows 9x era Microsoft Backup (MSBACKUP / MWBACKUP), early-to-mid 1990s |
SET conversions
Community Q&A
asked by usersFrequently asked questions
What is a .SET file?
It depends on the program. Historically it's a Microsoft Backup 'file set' (a definition of an old MS-DOS/Windows 9x backup job). Today a .set is most often just a settings/preferences file for some application (AutoCAD, Painter, games), or an EEGLAB dataset in research.
How do I open a .SET file?
Figure out which program created it (check the folder it's in) and let that program use it - .set files are usually loaded automatically, not opened by hand. To inspect an unknown one, open it in a text or hex editor.
Can I delete a .SET file?
If it's a program's settings file, deleting it usually just resets that program's options (it often recreates a default). Back it up first. A legacy backup .set only matters if you still need that old Microsoft Backup job.
How do I restore an old Microsoft Backup .SET?
You need the same era's Microsoft Backup utility (MS-DOS 6 / Windows 9x). Modern Windows tools can't read these; consider a virtual machine with the original OS if the data is critical.
Why does my game/design app have a .SET file?
It's storing its settings or a saved configuration there. Leave it alone unless you're intentionally resetting or transferring settings; the app reads it on its own.
How do I open an EEGLAB .SET file?
Use EEGLAB in MATLAB/Octave (pop_loadset). The .set holds the dataset structure and usually pairs with a .fdt file containing the raw data - keep them together.
References
1FileInfo - SET File Extensionfileinfo.com
2EEGLAB - Dataset (.set) file formatsccn.ucsd.edu
