| B | BASIC language source file |
| B_W | Atari/Macintosh black and white graphic |
| B&W | 1st Reader Mono binary screen image |
| B1N | 1st Reader Mono and color binary screen image |
| B30 | ABC Ventura publisher printer font |
| B4 | Helix Nuts and Bolts file |
| B8 | Raw graphic file (Piclab Plane II) |
| BAD | Oracle bad file |
| BAK | Backup file |
| BAL | Ballade Music score |
| BAND | Garageband Project song |
| BAR | dBase Application Generator Horizontal menu object |
| BAR | Game data file used with Age of Mythology and Age of Empires 3 |
| BAS | BASIC source code |
| BAT | Batch file |
| BB | Papyrus Database backup |
| BBL | TeX/BibTeX Bibliographic reference file |
| BBM | Deluxe Paint Bitmap image |
| BBS | Bulletin Board Sytem text |
| BCH | Datalex Entry Point 90 Data file |
| BCM | Microsoft Works Communications file |
| BCO | Bitstream Outline font description file |
| BCP | Borland C++ Makefile |
| BCW | Borland C++ 4.5 Environment settings file |
| BDB | Microsoft Works Dababase file |
| BDF | Egret Datafile |
| BDR | Microsoft Publisher Border |
| BEZ | Bitstream Outline font description |
| BF2 | Bradford 2 Font |
| BFC | Windows 95 Briefcase Document |
| BFM | Font Metrics file (Unix/Mainframe) |
| BFX | Fax document file (BitFax) |
| BG | Microsoft Backgammon Game file |
| BGA | OS/2 Graphic array |
| BGI | Borland Graphics Interface Driver |
| BGL | Microsoft Flight Simulator Scenery file |
| BHF | pcAnywhere Host file |
| BI | Binary file |
| BIB | TeX/BibTeX Literature Database |
| BIF | Image Capture Board Binary Image black & white graphic |
| BIFF | XLITE 3D file |
| BIG | Electronic Arts Game MOD File |
| BIN | Binary file |
| BIO | OS/2 Bios file |
| BIT | X11 Bitmap |
| BK | JetFax Faxbook file |
| BK! | WordPerfect for Windows Document backup |
| BK$ | Backup file (Generic) |
| BK1 | WordPerfect for Windows Timed backup file for document window 1 |
| BK2 | WordPerfect for Windows Timed backup file for document window 2 |
| BK3 | WordPerfect for Windows Timed backup file for document window 3 |
| BK4 | WordPerfect for Windows Timed backup file for document window 4 |
| BK5 | WordPerfect for Windows Timed backup file for document window 5 |
| BK6 | WordPerfect for Windows Timed backup file for document window 6 |
| BK7 | WordPerfect for Windows Timed backup file for document window 7 |
| BK8 | WordPerfect for Windows Timed backup file for document window 8 |
| BK9 | WordPerfect for Windows Timed backup file for document window 9 |
| BKP | TurboVidion Dialog Designer Backup |
| BKS | Microsoft Works Spreadsheet Backup |
| BKW | FontEdit Fontset mirror image |
| BLB | Resource archive (DreamWorks),(Neverhood) |
| BLD | BASIC Bloadable picture file |
| BLEND | Data file for Blender 3D modeling suite. |
| BLK | WordPerfect for Windows Temporary file |
| BM | Windows system Bitmap |
| BM1 | Apogee BioMenace data |
| BMA | Song format used by Beatmania emulators |
| BMF | Corel Gallery file |
| BMK | Windows Help bookmark |
| BMP | Windows or OS/2 bitmap |
| BN | Instrument bank file (AdLib) |
| BNK | Instrument Bank file (AdLib) |
| BOL | Compressed archive library file (Microsoft Booasm.arc) |
| BOM | Bill of materials file |
| BOO | Microsoft Booasm.arc Compressed archive |
| BOOK | Adobe FrameMaker Book |
| BOX | Lotus Notes file |
| BPC | Business Plan Toolkit Chart |
| BPL | Borland Delphi 4 packed library |
| BPS | Microsoft Works Document |
| BPT | CorelDraw Bitmap fills file |
| BPX | Truevision Targa Bitmap |
| BQY | BrioQuery file |
| BR | Bridge Script |
| BR0 | PrintMaster graphics file |
| BRD | Eagle Layout file |
| BRK | Brooktrout Fax-Mail file |
| BRW | Application file associated with financial institution(s) loan applications |
| BRX | A file for browsing an index of multimedia options |
| BRZ | DbBRZ file for very large Db backup or restore |
| BS_ | Microsoft Bookshelf Find Menu shell extension |
| BS1 | Apogee Blake Stone data file |
| BSA | BSARC Compressed archive |
| BSC | Fortran Pwbrmake Object |
| BSP | Quake map file |
| BTM | Batch file used by Norton Utilities |
| BTR | Database file (Btrieve 5.1) |
| BUD | Backup disk for Quicken |
| BUG | Bugs and Problems file |
| BUN | CakeWalk Audio Bundle (a MIDI program) |
| BUP | Backup |
| BUT | Buttons! Button definition |
| BUY | Movie data file |
| BV1 | WordPerfect for Windows Overflow file below insert point in document 1 |
| BV2 | WordPerfect for Windows Overflow file below insert point in document 2 |
| BV3 | WordPerfect for Windows Overflow file below insert point in document 3 |
| BV4 | WordPerfect for Windows Overflow file below insert point in document 4 |
| BV5 | WordPerfect for Windows Overflow file below insert point in document 5 |
| BV6 | WordPerfect for Windows Overflow file below insert point in document 6 |
| BV7 | Wordperfect for Windows Overflow file below insert point in document 7 |
| BV8 | WordPerfect for Windows Overflow file below insert point in document 8 |
| BV9 | WordPerfect for Windows Overflow file below insert point in document 9 |
| BW | Silicon Graphics Raw red,green and blue bytes file |
| BWB | Visual Baler Spreadsheet application |
| BWR | Kermit Beware buglist |
| BWV | Business Wave file |
| BYU | BYU Movie |
| BZ | Bzip compressed file (Inix) |
| BZ2 | Bzip compressed file (Unix) (replaces Bz) |
