DOS extender
To boot the system from CD-ROM, the FM TOWNS has a "hidden C:" ROM drive in which a minimum MS-DOS system, CD-ROM driver and MSCDEX.EXE are installed. This minimal DOS system runs first, and the DOS system reads and executes the Towns OS IPL stored in CD-ROM after that. The Towns OS CD-ROM has an IPL, MS-DOS system (IO.SYS), DOS extender, and Towns API (TBIOS).