| File extension Name |
extension description |
| .U | Unknown Apple II File (found on Golden Orchard Apple II CD Rom) |
| .U | Subsampled Raw YUV Bitmap |
| .U | Unreal System File |
| .U | Unreal Tournament 2003 System File (Epic Games, Inc.) |
| .U | Nitpicker Ipflow File |
| .U2 | Telelogic Tau UML Model |
| .U2E | Unreal Game Translation |
| .U2P | Telelogic Tau UML Program Text File |
| .U3D | Universal 3D File |
| .U3P | U3 Platform Install File (U3 LLC.) |
| .U4A | UnInstaller Archive |
| .U8 | Raw Unsigned 8-Bit Audio Data |
| .U96 | EasyZip Temporary File |
| .U98 | Urdu 98 Document |
| .UAE | WinUAE 0.8.22 Game Configuration File |
| .UAP | User Agent Wireless Telephony Profile |
| .UAS | PhotoImpact Backup/Recovery File (Ulead Systems, Inc.) |
| .UAX | Unreal Tournament 2003 Sound (Epic Games, Inc.) |
| .UAX | Unified Application eXchange Format (UAX Project) |
| .UAX | Deus Ex |
| .UAX | Harry Potter |
| .UAX | Rune |
| .UAX | Undying |
| .UAX | Unreal / Unreal 2 |
| .UAX | Unreal Audio File (Epic Games, Inc.) |
| .UB | Raw Unsigned Byte (8-bit) Data |
| .UB | Audio |
| .UBB | BASIC UBAS File |
| .UBD | BASIC UBAS File |
| .UBK | National Construction Estimator 32 User Costbook |
| .UBK | Embiid Reader eBook (Embiid Inc.) |
| .UBM | Iphoto Mtwain Install File |
| .UBS | Tracesrv Bugslayer Utility File |
| .UC | AutoCut Flash Firmware File (Autometrix) |
| .UC | Unreal Tournament Code File (Epic Games, Inc.) |
| .UC2 | UltraCompressor II Compressed Archive (AIPNL) |
| .UCC | National UCC Financing Statement Software Uniform Commercial Code Form (National LawForms, Inc.) |
| .UCD | Prosa/ OM Use Case Diagram |
| .UCE | UniCode Extensions |
| .UCF | Epson Personal Settings Information (Epson Corporation) |
| .UCF | Xilinx Foundation User Constraint File |
| .UCG | ULEAD MediaStudio CG Infinity Graphic (Corel Corporation) |
| .UCI | Samsung YP-P2 Theme |
| .UCM | Urban Chaos Game File |
| .UCMN | Unknown Apple II File (found on Golden Orchard Apple II CD Rom) |
| .UCN | U-Act Configurator Configuration Storage File (Unisys) |
| .UCN | Compressed Archive |
| .UCR | MicroSim PCBoard Unrouted Nets Report |
| .UCS | Homeworld Localized Unicode Strings (Sierra Entertainment, Inc.) |
| .UCS | Universal Classification Standard Database File |
| .UCX | Rational XDE (IBM) |
| .UD | OmniPage User Dictionary (Nuance Communications, Inc.) |
| .UD | AOL 4.0 (America Online, Inc.) |
| .UDB | Windows2000 Uniqueness Database File (Microsoft Corporation) |
| .UDB | Works File (Microsoft Corporation) |
| .UDB | PINO 3-Server File |
| .UDB | VBA32 Antivirus Signature File (VirusBlokAda Ltd.) |
| .UDC | Acrobat Spelling File (Adobe Systems Incorporated) |
| .UDC | Fh5 US English File |
| .UDC | Systems Management Server (SMS) Collection Evaluator Updates Collection (Microsoft Corporation) |
| .UDD | OllyDbg Module Information (Oleh Yuschuk) |
| .UDF | Excel User Defined Function (Microsoft Corporation) |
| .UDF | Photostyler Image Filter |
| .UDF | Windows NT Uniqueness Database File |
| .UDF | X-ray Diffraction Data File Format |
| .UDI | Corel Graphics Ver 10 Draw Script Textures Bitmap File (Corel) |
| .UDI | Dazzle DVD Complete (Pinnacle Systems, Inc.) |
| .UDL | Data Link (Microsoft Corporation) |
| .UDL | ADONIS User Export From Database (BOC Group) |
| .UDM | MapView User-Defined Module (MotCreations) |
| .UDS | NHTSA UDS-1992 Crash Test Data |
| .UDS | FIMware Database (Uniform Data System for Medical Rehabilitation, a division of UB Foundation Activities, Inc.) |
| .UDS | Sierra Generations Geneology Family File (Sierra Entertainment, Inc.) |
| .UDW | Raw Unsigned DoubleWord (32-bit) Data |
| .UE2 | Encrypted Archive |
| .UEED | Uconomix Encryption Engine Encrypted Directory (Uconomix Technologies Pvt Ltd) |
| .UEEF | Uconomix Encryption Engine Encrypted File (Uconomix Technologies Pvt Ltd) |
| .UEF | Unified Emulator Format |
| .UENC | UltraEdit Encrypted File (IDM Computer Solutions, Inc.) |
| .UEZ | COOL 3D (Ulead Systems, Inc.) |
| .UFA | UFA Compressed File Archive |
| .UFA | GIF Animator Animation Object Information (Ulead) |
| .UFD | PDP-10 User File Directory |
| .UFF | DataWave Physiological Data File |
| .UFI | UFOCaptureV2 Presets (SonotaCo) |
| .UFO | Ellisys Visual USB Data (Ellisys) |
| .UFO | Total Annihilation Third-party Unit (Cavedog Entertainment) |
| .UFO | PhotoImpact Graphic (Ulead Systems, Inc.) |
| .UFSD | UFS Explorer Professional Recovery RAW Recovery Signatures Database (SysDevSoftware) |
| .UG | Drawing File |
| .UGA | Ulead GIF Animator Project File (Corel Corporation) |
| .UH | Age of Kings (Microsoft Corporation) |
| .UHA | UHARC Compressed Archive |
| .UHS | Universal Hint System File (Universal Hint System) |
| .UHTM | Unreal Tournament File |
| .UI | Geoworks UI Compiler Espire Source |
| .UI | User Interface |
| .UI | Qt User Interface (Qt Software) |
| .UID | IBM Voice Type Users File (IBM) |
| .UIF | WordPerfect Long Prompts (Corel Corporation) |
| .UIF | Magic ISO Universal Image Format File (MagicISO Inc.) |
| .UIH | Geoworks UI Compiler Espire Header |
| .UIL | X-Motif UIL Table |
| .UIN | ICQ 2001+ Saved ICQ Contact Information (ICQ Inc.) |
| .uindex | Newsgroup Index File |
| .UIR | LabWindows User Interface Resource (National Instruments Corporation) |
| .UIS | WindowBlinds Skin |
| .UKA | Fifa World Cup Game Data fe Art Legalscr File |
| .UKA | UKA Data Archive (HRM Systems AG, CH-Winterthur) |
| .UKS | Works File (Microsoft Corporation) |
| .UKX | Unreal Tournament 2003 Animation (Epic Games, Inc.) |
| .UK_ | Mcguiness File |
| .UL | uLAW Audio File |
| .ULD | Procomm Uploaded Files |
| .ULF | Uniware Layout File (Uniware) |
| .ULP | Peugeot Diag 2000 File |
| .ULP | EAGLE Layout Editor Script (CadSoft Computer GmbH) |
| .ULS | Internet Location Service |
| .ULT | UltraTracker Music Module |
| .ULW | ULAW - Sun/NeXT |
| .ULX | CLAN Lexical File (Child Language Data Exchange System) |
| .ULX | Glulx Game |
| .UM | Unknown Apple II File (found on Golden Orchard Apple II CD Rom) |
| .UM | The Land Of UM World File |
| .UMB | MemMaker Backup Archive |
| .UMD | UMD Photobook |
| .UMI | CDDB Database and PC Music Library in PlayCenter |
| .UML | Visual UML Class Diagram & Model (Visual Object Modelers, Inc.) |
| .UMOD | Unreal Self-extracting MOD File (Epic Games) |
| .UMOD | Unreal Tournament (Epic Games, Inc.) |
| .UMP | UModel Project (Altova) |
| .UMR | MyEclipse UML Model Repository (Genuitec, LLC.) |
| .UMS | Rune |
| .UMX | Unreal/Unreal Tournament Music File (Epic Games, Inc.) |
| .UMX | Deus Ex |
| .UMX | Harry Potter |
| .UMX | U-MYX Player Song Mix Data and Timing Info (U-MYX Ltd.) |
| .UMX | Unreal Tournament 2003 Music (Epic Games, Inc.) |
| .UNASSIGNED | Unknown Apple II File (found on Golden Orchard Apple II CD Rom) |
| .UNC | Files and Settings Transfer Wizard Output Folder (Microsoft Corporation) |
| .UNCIAL | Unknown Apple II File (found on Golden Orchard Apple II CD Rom) |
| .UND | A86 Assembler Undefined Symbols |
| .UNF | Btreive Unformatted File |
| .UNI | Forcast Pro Data File |
| .UNI | MikMod (UniMod) Format |
| .UNIKEY | Unikey Software Protection Solution (SecuTech Solution Inc.) |
| .UNION | Unknown Apple II File (found on Golden Orchard Apple II CD Rom) |
| .UNIVERSAL3 | Unknown Apple II File (found on Golden Orchard Apple II CD Rom) |
| .UNIX | UNIX File |
| .UNIX | Unknown Apple II File (found on Golden Orchard Apple II CD Rom) |
| .UNKNOWN | [None] |
| .UNL | Informix Binary File Created by UNLOAD Command |
| .UNLOCK | Unknown Apple II File (found on Golden Orchard Apple II CD Rom) |
| .UNM | XMap Flight Plan or Flight Plan Statistic File (Delorme) |
| .UNPAC | Unknown Apple II File (found on Golden Orchard Apple II CD Rom) |
| .UNPACK | Unknown Apple II File (found on Golden Orchard Apple II CD Rom) |
| .UNQ | ACT! Saved Unknown Attachment (Best Software CRM Division) |
| .UNQ | Fax View File |
| .UNR | Unreal Map File |
| .UNS | Visual Navigation Suite Export/Import Settings (Jeppesen Marine, Inc.) |
| .UNT | AutoCAD Unit Definition (Autodesk, Inc.) |
| .UNUSED | Photoline4 Defaults File |
| .UNV | Forecast Pro Univariate Forecast File (Business Forecast Systems, Inc.) |
| .UNV | SDRC I-DEAS File |
| .UNV | BusinessObjects/WebIntelligence Universe File |
| .UNX | Unknown Apple II File (found on Golden Orchard Apple II CD Rom) |
| .UNX | Text File |
| .UN_ | Ntgraph Setup30 file |
| .UOF | Uniform Office Format |
| .UOL | PhotoImpact Object Library File |
| .UP | Unknown Apple II File (found on Golden Orchard Apple II CD Rom) |
| .UP2 | Cool3d Plug-ins Board File |
| .UPC | Ultimate Paint (J-T-L Development Inc.) |
| .UPCASE | Unknown Apple II File (found on Golden Orchard Apple II CD Rom) |
| .UPD | dBASE Update File |
| .UPD | VideoStudio Scene Information (Ulead Systems, Inc.) |
| .UPD | ProUpdater Per/Directory Options Setting File |
| .UPD | Ulead Private Data (Corel Corporation) |
| .UPD | Unknown Apple II File (found on Golden Orchard Apple II CD Rom) |
| .UPD | Updated Program Data |
| .UPD | Universal Print Driver |
| .UPDATE | Program or Data File Update |
| .UPDATE | Unknown Apple II File (found on Golden Orchard Apple II CD Rom) |
| .UPDATE | ISAPI Loader New ISAPI Application (EGGcentric) |
| .UPDATEALL | Unknown Apple II File (found on Golden Orchard Apple II CD Rom) |
| .UPDATEINFO | Unknown Apple II File (found on Golden Orchard Apple II CD Rom) |
| .UPDATES | Unknown Apple II File (found on Golden Orchard Apple II CD Rom) |
| .UPDF | UltraPdf Publication (Software995) |
| .UPF | Nokia Phone Digital Photo (Nokia) |
| .UPF | Universal Picture Format Bitmap |
| .UPG | Grafik Anim File |
| .UPG | Firmware Upgrade File |
| .UPI | Iphoto4 Programs Plug-in File |
| .UPI | ULead Photo Impact Program File (Corel Corporation) |
| .UPJ | ULead Project File (Corel Corporation) |
| .UPK | Mass Effect Game File Archive (EA International (Studio and Publishing) Ltd.) |
| .UPL | Starmoney Agent Download File |
| .UPL | Unknown Apple II File (found on Golden Orchard Apple II CD Rom) |
| .UPM | PenMail Document (UC-Logic Technology Corp.) |
| .UPO | dBASE Compiled Update File |
| .UPP | Uniprint Unified Printer Parameter |
| .UPR | FileMaker User Spelling Dictionary |
| .UPS | Works File (Microsoft Corporation) |
| .UPT | Connectivity Memory Model Update Timing Input File |
| .UPX | ULead Photo Express Saved Image File (Corel Corporation) |
| .UPZ | Starmoney Agent Download File |
| .UQM | The Ur-Quan Masters Archive (The Ur-Quan Masters Team) |
| .URBS | Unknown Apple II File (found on Golden Orchard Apple II CD Rom) |
| .URD | Ultra Recall Database (Kinook Software, Inc.) |
| .URD-JOURNAL | Ultra Recall Journal Update File (Kinook Software, Inc.) |
| .URF | ProWORX Nxt User Configurable Register Editor File (Schneider Electric) |
| .URF | Radar ViewPoint Universal Radar Format |
| .URF | AppFace Skin (Matinsoft Inc.) |
| .URI | List of Uniform Resource Identifiers |
| .URIS | List of Uniform Resource Identifiers |
| .URL | Internet Location |
| .URLS | GetRight URL List (Headlight Software, Inc.) |
| .URS | ControlDraw User Requirements Specifier (ControlDraw Ltd.) |
| .URT | Utah Raster Image |
| .US | Unknown Apple II File (found on Golden Orchard Apple II CD Rom) |
| .USA | Office Header File (Microsoft Corporation) |
| .USA | Unreal Saved Game File |
| .USAGE | Snort File |
| .USAGE | Unknown Apple II File (found on Golden Orchard Apple II CD Rom) |
| .USB | USB Protocol Analyzer Trace |
| .USB | Syssoft Sandra File |
| .USB | D-Link FM Radio Update |
| .USD | Epson PRINT Image Framer (PIF) Framer File (Seiko Epson Corp.) |
| .USE | Unknown Apple II File (found on Golden Orchard Apple II CD Rom) |
| .USE | MKS Source Integrity File |
| .USE | Log File |
| .USER | Unknown Apple II File (found on Golden Orchard Apple II CD Rom) |
| .USERPROFILE | Live Update User Profile (Symantec Corporation) |
| .USF | Nintendo Ultra 64 Sound Format (Nintendo) |
| .USF | Core Media Player XML Universal Subtitle Format File (CoreCodec, Inc.) |
| .USI | UsiXML UI Description File (Universite Catholique de Louvain-la-Neuve) |
| .USI | Unknown Apple II File (found on Golden Orchard Apple II CD Rom) |
| .USL | LaserJet Landscape Font |
| .USL | PC-Bibliothek User Dictionary (Bibliographisches Institut & F.A. Brockhaus AG) |
| .USL | ProWORX Nxt USL Loadables (Schneider Electric) |
| .USP | LaserJet Portrait Font |
| .USP | SIMCA-P/SIMCA-P+ Project (Umetrics AB) |
| .USP | PageMaker Printer Font (Adobe Systems Incorporated) |
| .USR | Unknown Apple II File (found on Golden Orchard Apple II CD Rom) |
| .USR | Uplink Player Information File (Introversion Software) |
| .USR | User Database |
| .USR | ERGO Receiver Configuration File (Creative Express Corporation) |
| .USR | MicroImages User-specific Information (MicroImages, Inc.) |
| .USR | FileMaker Pro Runtime Engine Database Application (FileMaker, Inc.) |
| .USR | Pegasus Mail User Information (David Harris) |
| .USR | Photo Paint User Defined Filter (Corel) |
| .USR | Daqarta Extended Audio Data (Interstellar Research) |
| .USS | PhotoImpact Exported Slicing Pattern (Ulead Systems, Inc.) |
| .USS | WinUAE Saved State |
| .UST | WiFi SiStr Exported User Theme (DNsoft.be) |
| .USTAR | POSIX tar Compressed Archive |
| .USX | Unreal Tournament 2003 Static Mesh (Epic Games, Inc.) |
| .USYM | Unknown Apple II File (found on Golden Orchard Apple II CD Rom) |
| .USZ | UsiXML UI Description File (Universite Catholique de Louvain-la-Neuve) |
| .UT2 | Unreal Tournament Map (Epic Games, Inc.) |
| .UT2MOD | Unreal Tournament 2003 Game Modification File (Epic Games) |
| .UT3 | Unreal Tournament 3 Map (Epic Games, Inc.) |
| .UT4MOD | Unreal Tournament 2004 MOD Installation Package (Epic Games) |
| .UTC | BioWare Aurora Engine Creature (BioWare Corp.) |
| .UTD | BioWare Aurora Engine Doors (BioWare Corp.) |
| .UTE | Rukus 110 File |
| .UTE | BioWare Aurora Engine Encounter (BioWare Corp.) |
| .UTF | AOL Updating Files (America Online, Inc.) |
| .UTI | BioWare Aurora Engine Item (BioWare Corp.) |
| .UTI | Spybot - Search & Destroy Usage Tracking (PepiMK Software) |
| .UTI | SafeGuard PrivateCrypto Encrypted Archive (Utimaco Safeware AG) |
| .UTIL | Unknown Apple II File (found on Golden Orchard Apple II CD Rom) |
| .UTIL2 | Unknown Apple II File (found on Golden Orchard Apple II CD Rom) |
| .UTILITIES | Unknown Apple II File (found on Golden Orchard Apple II CD Rom) |
| .UTILITY | Unknown Apple II File (found on Golden Orchard Apple II CD Rom) |
| .UTILS | Unknown Apple II File (found on Golden Orchard Apple II CD Rom) |
| .UTL | QuickBooks Data (Intuit Inc.) |
| .UTL | Sound File |
| .UTM | BioWare Aurora Engine Store (BioWare Corp.) |
| .UTMP | Unknown Apple II File (found on Golden Orchard Apple II CD Rom) |
| .UTP | BioWare Aurora Engine Placeable Object (BioWare Corp.) |
| .UTP | BinPatch Patch Data File |
| .UTS | BioWare Aurora Engine Sound (BioWare Corp.) |
| .UTS | Spybot - Search & Destroy Include File (PepiMK Software) |
| .UTT | BioWare Aurora Engine Trigger (BioWare Corp.) |
| .UTW | BioWare Aurora Engine Waypoint (BioWare Corp.) |
| .UTX | Rune |
| .UTX | Undying |
| .UTX | Harry Potter |
| .UTX | Deus Ex |
| .UTX | Unreal Tournament 2003 (or UT 99) Texture (Epic Games, Inc.) |
| .UTX | Unicode File |
| .UU | Compressed Archive File |
| .UUCP | Unknown Apple II File (found on Golden Orchard Apple II CD Rom) |
| .UUD | Uudecoded |
| .UUE | Unknown Apple II File (found on Golden Orchard Apple II CD Rom) |
| .UUE | Uuencoded |
| .UUT | Genesis 2000 (Genesis 2000, Inc.) |
| .UV | EA Games Video File (Electronic Arts, Inc.) |
| .UV2 | Jane's Combat Simulations F-15 |
| .UVP | ULEAD MediaStudio Video Paint Graphic (Corel Corporation) |
| .UVR | Ulead Cool 360 Viewer File (Corel Corporation) |
| .UVV | Listlabl File |
| .UVW | geoManager/geoInterface User View |
| .UVX | Unreal Tournament 2003 Saved Game (Epic Games, Inc.) |
| .UW | Unitype GlobalWriter File |
| .UW | Raw Unsigned Word (16-bit) Data |
| .UW | Audio |
| .UWF | UltraTracker Wave File |
| .UWL | GroupWise User Word List (Novell, Inc.) |
| .UWL | WordPerfect User Word List (Corel Corporation) |
| .UWS | UniTrader 2006 Website Archive (UniTechnology Limited) |
| .UWT | UniTrader Template Archive (UniTechnology Ltd.) |
| .UX | UNIX File |
| .UXD | URLBase URL Database (Terria Development) |
| .UXF | UMLet UML eXchange Format (UMLet Team) |
| .UXP | URLBase URL Database (v. 5.1) (Terria Development) |
| .UXX | Unreal Tournament 2003 Cache (Epic Games, Inc.) |
| .UXY | Orchida Embroidery System (Orchida Soft) |
| .UYVY | ImageMagick Ver. 5.3.2 Perlmagick File (ImageMagick Studio LLC) |
| .UYVY | Interleaved YUV Raw Image |
| .UZ | Unreal Tournament Server File |
| .UZE | Ultimate Zip Compresion Agent |
| .UZR | UZR 3D Streamable 3D File Format |