U = Bitmap image : subsampled raw YUV file
    U4A = UnInstaller archive
    U8 = Sample
    U96 = EasyZip Temporary File
    U98 = USA 98: Streets & Dest. Tour
    UAP = WAP applications "User Agent Profile"
    UAX = Unreal Audio File
    UB = Music file (uchar)
    UBB = Basic Ubas file
    UBD = Basic Ubas file
    UBI = Animation UBISOFT
    UBM = Iphoto Mtwain Install file
    UBS = Tracesrv etc Bugslayer util file
    UC0 = Archive UC
    UC2 = UltraCompressor II compressed archive
    UCD = Prosa/ OM Use Case Diagram
    UCE = WINXP SYSTEM32 file
    UCM = Urban Chaos Game File
    UCN = UltraCompressor II compressed archive
    UCR = pixel image file
    UD = Aol40 file
    UDB = Msworks file
    UDC = Fh5 Usenglsh file
    UDF = Photostyler filter
    UDF = Windows NT Uniqueness Database File
    UDI = Corel Graphics10 Draw Skripts textures Bitmap file
    UDL = MS Data Link
    UDO = 3d Graphic
    udog = (MAC FILE_TYPE) Apple Browser Launcher
    UDP = User Datagram Protocol
    UDT = UDTDemo.Document open with: UDTDEMO.EXE /dde
    UDW = Raw Unsigned DoubleWord (32-bit) Data
    UE2 = UltraCompressor II encrypted file archive
    UFA = UFA compressed file archive
    UFDL = Mime: application/vnd.ufdl
    UFO = Ulead File for Objects (Ulead PhotoImpact)
    UG = AutoCAD and others : Drawing file
    ugbt = (MAC FILE_TYPE) Users & Groups
    UHS = Universal Hint System (binary file)
    UI = Espire language source (Geoworks UI Compiler)
    UI = User Interface (Sprint)
    UID = "IBM Voice Type" Users file
    UIF = WordPerfect for Win long prompts for Windows
    UIH = Espire header file (Geoworks UI Compiler)
    UIL = Bitmap image (X-Motif UIL icon file)
    UIL = Mime: text/x-uil
    UIN = ICQ (a variety of instant messaging) user
    UIS = WindowBlinds Skin
    UK = TAGCASE0 html folder file
    UK_ = Mcguiness file
    UKA = Fifa World Cup game data fe art Legalscr file
    UKS = Msworks file
    UL = Ulaw music file
    ULAW = (MAC FILE_TYPE) AU Soundyer Plug-in Filau
    ULAW = sound file
    ULD = Procomm Plus uploaded file information
    ULS = Internet; User Location Service (Internet New Media Phone)
    ULT = Ultratracker music module (MOD) file
    UMB = Backup by MemMaker
    UMOD = Unreal Self-extracting MOD File
    UMX = Unreal Game Data File
    UN_ = Ntgraph Setup30 file
    UND = A86 UNDefined symbols
    UNI = Forecast Pro datafile
    UNI = Mime: text/uri-list
    UNI = Music (UniMOD/MikMOD)
    UNIC = Unic Tracker v1/v2 formats (music/sound)(Asle / ReDoX)
    UNIS = Mime: text/uri-list
    UNIX = Unix file
    UNIXYZ = UniChem chemical modeller output file
    UNIXYZ = UniChem XYZ chemical modeller input file
    UNPA* = glslang unpack program(* means only .unpa is tested)
    UNQ = ACT! 3.0 Email message attachment
    UNR = Unreal Game Data File
    UNT = Unit
    UNUSED = Photoline4 Defaults file
    UNV = Mime: application/i-deas
    UNV = SDRC I-DEAS file
    UNX = Text file containing UNIX specific info
    UOL = PhotoImpact Clipart Images
    UP2 = Cool3d plugins board file
    UPC = Ultimate Paint component
    UPD = UPDate info
    UPF = Bitmap image (Universal Picture Format)
    UPG = Grafik Anim file
    UPI = Iphoto4 Programs Plugin file
    UPJ = ULead Project File
    UPL = Starmoney Agent Download file
    UPO = dBASE compiled update data
    UPR = Claris user dictionary
    UPS = Msworks file
    UPX = ULead Photo Express Saved Image File
    UPZ = Starmoney Agent Download file
    URF = "Radar ViewPoint" universal radar format
    URI = List of Uniform Resource Identifiers (WWW)
    URI = Mime: text/uri-list
    URIS = List of Uniform Resource Identifiers (WWW)
    URIS = Mime: text/uri-list
    URL = Internet Shortcut
    URL = Universal Resource Locator/internet
    URL_ = (MAC FILE_TYPE) Web Site Address-in Fiurl
    URLS = Mime: application/x-url-list
    URLS = Universal Resource Locator : List of Internet shortcuts
    URT = Bitmap image (Utah Run-Length Encoded image file)
    US? = MS Word for DOS/WordPerfect Font
    USA = Microsoft Office Headers file
    USAGE = Snort file
    USB = Syssoft Sandra file
    USE = gen. Log
    USE = MKS Source Integrity file
    USERPROFILE = Symantec Shared file
    USL = LaserJet Landscape Font
    USM = Audio: Unsigned Sample Module data Farandole
    USP = PageMaker printer font with US Ascii extended character set
    USR = User database (Procomm Plus/Turbo C++ tour)
    USRP = UTM/Universe Polar Stereographic (UPS) (USRP/ASRP 1.1/1.2),(French Defense Mapping Agency)
    USTAR = Mime: application/x-ustar
    USTAR = Mime: multipart/x-ustar
    USTAR = POSIX tar compressed archive
    utbl = (MAC FILE_TYPE) Text Encoding
    UTE = Rukus 110 file
    UTF = AOL Updating Files (in "Tools on Demand" folder)
    UTI = Spybot Includes file
    UTL = QuickBooks data
    UTP = BinPatch Patch Data File
    UTS = Spybot Includes file
    UTX = Unreal Texture File
    utxt = (MAC FILE_TYPE) Unicode Text File
    UU = Encoded file archive (ascii) (uudecode/uuencode)
    UU = Mime: application/octet-stream
    UU = Mime: application/uue
    UU = Mime: text/x-uuencode
    UUD = Encoded file archive (ascii) (uuencode)
    UUE = Mime: application/uue
    UUE = Mime: text/x-uuencode
    UUE = UUEncoded file.Ascci encoded file for binary attachments
    UVR = Ulead Cool 360 Viewer File
    UVV = Listlabl file
    UW = unsigned word Music file
    UWF = UltraTracker WaveSample music file
    UWL = WordPerfect User Word List
    UX = Unix file
    UYVY = Imagemagick-5.3.2 Perlmagick file
    UYVY = YUV 16Bits image format