| 1. | B | Basic language source code file Modula-3 base program APPLAUSE Batch list |
| 2. | B&W | Black & White bitmap image (atari - mac) 1st Reader bitmap image (mono binary screen image) |
| 3. | B1N | 1st Reader bitmap image (both mono and color binary screen image) |
| 4. | B30 | Printer font (JLaser - Cordata) (Ventura Publisher) |
| 5. | B4 | Helix Nuts and Bolts file |
| 6. | B64 | StuffItEncoded encoded file archive (ascii) (base64 MIME) |
| 7. | B8 | PicLab bitmap image (one byte per pixel) plane two Cubicomp PictureMaker red channel image data (24bit 3D animation) |
| 8. | BAC | |
| 9. | BAD | |
| 10. | BAK | Often used as BAcKup file. |
| 11. | BAL | |
| 12. | BAR | Unix BAR compressed file archive dBASE Application Generator horizontal bar menu object file |
| 13. | BAS | Basic source. Often readable with Notepad |
| 14. | BAT | MS-DOS batch file (Executable) |
| 15. | BB | |
| 16. | BBL | TeX/BibTeX BiBLiographic reference |
| 17. | BBM | Deluxe Paint bitmap image, used for animations |
| 18. | BBNNG | Bitmap image (BBN BitGraph terminal Display Pixel Data (DPD) sequence) |
| 19. | BBP | |
| 20. | BBS | Text from Bulletin Board System Hudson-style messagebase (FTN software) |