B

File extensions starting with the letter B...

  .B    Limbo Implementation File (Inferno OS)
        Applause Batch List
  .B1J  BookJones
  .B1N  1st Reader Binary Screen Image
  .B1S  BookSmith
  .B30  Ventura Publisher Printer Font
  .B3D  3D Builder File
  .B4   Helix Nuts and Bolts File (Helix Software now part of McAfee)
  .B64  Base 64 MIME-encoded File  [MIME]
  .B8   Piclab Raw Graphic File

  .BAC  Backup
  .BAD  Rime Mailer Address File
        Oracle BAD File
  .BAK  Backup
  .BAL  Ballade Music Score
  .BAR  dBase Application Generator Horizontal Menu Object
  .BAS  BASIC Language Source
        Basic Module
  .BAT  Batch Processing
  .BB   Papyrus Database Backup
  .BB2  XBBS-OS/2, XGROUP, AV and ZTree Archiver Control File
  .BBL  TeX/BibTeX Bibliographic Reference File
  .BBM  Deluxe Paint Image File
  .BBS  Bulletin Board Sytem Text
  .BCF  ConfigSafe Snapshot Index
  .BCH  dBase Application Generator Batch Process Object
        Phoenix Software (Datalex) Entry Point 90 Data File
  .BCK  Backup
  .BCM  MS Works Communications File
  .BCO  Bitstream Fontware File
  .BCP  Borland C++ Makefile
  .BCW  Borland C++ 4.5 Environment Settings
  .BDB  MS Works Dababase File
  .BDF  West Point Bridge Designer File
  .BDF  Egret Data File
  .BDR  MS Publisher Border
  .BEZ  Bitstream Fontware File
  .BF2  Bradford 2 Font
  .BFA  Blowfish-encrypted File (Extension added to original) [Program List]
  .BFC  Briefcase File
  .BFF  AIX® Backup File Format
  .BFM  UNIX Font Metrics File
  .BFX  BitFax Document
  .BG   MS Backgammon for Windows Game
  .BGA  OS/2 Graphic Array
  .BGB  MS Chat Background Graphic
  .BGI  Borland Graphic Interface
  .BGL  Flight Simulator Scenery File
  .BHF  pcAnywhere Host File
  .BI   Binary File
        Progress Database Before Image File
  .BIB  Bibliography
        TeX/BibTeX Literature Database
  .BIF  GroupWise Initialization File
        Image Capture Board Binary Black & White Image
  .BIG  Chinese (old version)
  .BIK  BioCharter Profile Backup File
  .BIN  Binary File
  .BIO  BioCharter Profile File
        OS/2 Bios File
  .BIT  Bitmap Image  
  .BK   Backup
        LinguAssist File
        JetFax Faxbook File
  .BK!  Backup
  .BK$  Backup
  .BK1  Backup (Can be 1 to 9, usually with WordPerfect)
  .BKI  Backup Index
  .BKP  Backup  
  .BKS  Bookshelf Backup
        IBM BookManager Read Bookshelf
        MS Works Spreadsheet Backup
  .BKW  FontEdit Fontset Mirror Image
  .BLB  DreamWorks Resource Archive 
  .BLD  BASIC Bload Graphics
  .BLK  WordPerfect Temp File
        Lightscape Block Library
        Alias Wavefront Image
  .BLL  An extension used by the VBS/European-A worm. If found in the directory
          C:\STARTUP suspect you are infected with this worm and have your computer
          checked with anti-virus software!
  .BLT  Wordperfect for DOS File
  .BM   Graphic (bitmap)
  .BM1  Apogee BioMenace Data File
  .BMF  Image File  
  .BMI  Buzz Instrument
  .BMK  Help Bookmark
  .BMP  Windows OS/2 Bitmap Graphics  [Viewer]
  .BMS  Backup Magic Backup Set
  .BMW  Buzz Music File with Waves
  .BMX  Buzz Music File
  .BN   AdLib Instrument Bank
  .BNK  Adlib Instrument Bank
        SimCity Game File
        (reported to be) Bink Compressed Video/Audio File
  .BOL  MS Booasm Compressed Archive Library
  .BOM  Orcad Schematic Capture Bill of Materials File
  .BOO  Image File
        Book
        Compressed Archive File  
  .BOX  Notes Mailbox
  .BPC  Business Plan Toolkit Chart
  .BPL  Delphi Library
  .BPS  MS Works Document
  .BPT  Bitmap Master File
  .BPX  Truevision Targa Bitmap
  .BQY  BrioQuery File
  .BR   Bridge Script
  .BR3  Bryce 3D Scene File
  .BRC  Bryce 2 Scene File
  .BRD  EAGLE Board File
  .BRI  Basic Rate Interface File
  .BRK  Brooktrout Fax-Mail File
  .BRO  Tree Professional Broadleaf Creator File
  .BRP  Tree Professional Broadleaf Creator Image
  .BRW  Application file associated with financial institution(s) loan applications
  .BRX  Multimedia Browsing Index
  .BRZ  DbBRZ File (Backup or Restore)
  .BS_  MS Bookshelf Find Menu Shell Extension
  .BS1  Apogee Blake Stone Data File
  .BS2  Basic Stamp 2 Code File (WordPad or BS2-Editor)
  .BSA  BSARC Compressed Archive
  .BSC  Apple II Compressed Archive
        Fortran Pwbrmake Object
        Boyan Script
        MS Developer Studio Browser File
  .BSK  Bryce 4 File
  .BSP  Quake Map
        Half-life/TFC/CS Map
  .BSV  BASIC Bsave Graphics
  .BTM  4DOS Batch To Memory Batch File
  .BTN  ButtonWare File
  .BTR  Btrieve Database File
        MS Frontpage-related File
  .BUD  Quicken Backup
  .BUG  Bug (Problem) File
  .BUN  CakeWalk Audio Bundle File
  .BUP  Backup
  .BUT  Buttons! Button Definition
  .BUY  Movie Data File
  .BV1  WordPerfect Overflow File (Can be 1 to 9)
  .BVS  BVS Solitaire Collection
  .BW   SGI Black and White Image
        Silicon Graphics Raw RGB File
  .BWB  Visual Baler Spreadsheet File
  .BWR  Kermit Beware Bug List
  .BWV  Business Wave File
  .BYU  Movie File
  .BZ   Bzip UNIX Compressed File
  .BZ2  Bzip UNIX Compressed File (Replaces .BZ)