The file, "NSDOS-51-SDC-ALTAIR.NSI" is North Star DOS 5.1 for the single-density FDC with the operator console connected to an Altair 88-2SIO serial board. The disk image includes BASIC, floating point BASIC, monitors, and other utilities.

The file "NSDOSIO.ASM" contains the code that was used to patch North Star DOS for the Altair 88-2SIO board.