BAK Backup file

BAS BASIC code

BAT Batch file

BFC Windows 95 Briefcase document

BG Backgammon for Windows game

BI Binary file

BIF GroupWise initialization file

BIN Binary file

BK Sometimes used to denote backup versions

BK$ Also sometimes used to denote backup versions

BKS An IBM BookManager Read bookshelf

BMK An A bookmark file

BMP Windows or OS/2 bitmap

BM1 Apogee BioMenace data file

BRX A file for browsing an index of multimedia options

BSP Quake map

BS1 Apogee Blake Stone data file

BTM Batch file used by Norton Utilities

B4 Helix Nuts and Bolts file