for, loads, and executes a file named SOS.KERNEL, which is the kernel and API of the operating system. The kernel, in turn, searches for and loads a file named SOS.INTERP (the interpreter, or program, to run) and SOS.DRIVER, the set of device drivers to use. Once all files are loaded, control is passed to the SOS.INTERP program.

Apple ProDOS uses the same file system