BSX files store output data generated by PBASIC programming language preprocessor. PBASIC is a fork of BASIC language aimed at microcontrollers and embedded devices.

BSX format was released in 1992 by Parallax. Compiled PBASIC code is stored in EEPROM memory where it can be accessed by the device. BSX are now considered obsolete, and the last microcontroller that used solution similar to BSX files was the popular microcontroller PICAXE, released in 1999.