List of Data File Formats Starting with the Letter "U"
| .uax | Unreal Audio file |
| .ub | Audio file (unsigned byte) |
| .uc2 | Compressed file archive created by UltraCompressor II (uc2.zip) |
| .ucn | New compressed file archive created by UltraCompressor II |
| .ucs | Universal Classification Standard Database file |
| .udc | Acrobat Spelling file |
| .udf | Filter (Photostyler) |
| .udl | MS Data Link |
| .uds | Sierra Generations Family file |
| .ue2 | Encrypted file archive created by UltraCompressor II |
| .ufo | Ulead PhotoImpact Graphic file |
| .uha | UHARC Compressed Archive file |
| .uhs | Universal Hint System (binary file) |
| .ui | Espire source code file (Geoworks UI Compiler) |
| User interface (Sprint) | |
| .uif | MagicISO Disc Image file |
| Long prompts for windows (WordPerfect for Win) | |
| .uih | Espire header file (Geoworks UI Compiler) |
| .uis | WindowBlinds (Copyright Neil Banfield & Stardock.net, Inc.) |
| .ul | Ulaw audio file |
| .uld | Information about uploaded files (Procomm Plus) |
| .ult | Music (UltraTracker) |
| .umb | Backup file (MemMaker) |
| .umd | Universal Media Disc file |
| .umf | Stockmoves, MOTEK BV |
| .umx | Unreal music file |
| .uni | Unimod music module (MIKMOD) |
| Datafile (Forecast Pro) | |
| .unl | Garmin Unlock file |
| .unq | Fax View file |
| .uns2 | Ultra Notes Backup file |
| .unx | Text file containing UNIX specific info |
| .upd | Program update info |
| Update data (dBASE) | |
| .upg | Firmware Upgrade file |
| .upo | Compiled update data (dBASE) |
| .upx | ULead Photo Express Saved Image file |
| .url | Uniform Resource Locator (Internet shortcut) |
| .urls | GetRight URL List file |
| .usb | D-Link FM Radio Update |
| USB Protocol Analyzer Trace | |
| .user | Visual Studio User Options file |
| .usp | Printer font with USASCII extended character set (PageMaker) |
| .usr | User database file (Procomm Plus - Turbo C++ tour) |
| .utf | AOL Updating Files |
| .utl | Sound file |
| .utx | Unreal Engine Texture file |
| Unicode file | |
| .uu | Compressed ASCII file archive created by UUDE/ENCODE |
| .uue | Compressed ASCII file archive created by UUENCODE (uuexe515.exe) |
| .uvf | CSV (comma separated value) format. Used by Netica |
| .uvr | Ulead Cool 360 Viewer file |
| .uw | Audio file (unsigned word) |
| .uwl | WordPerfect User Word List file |
