It is even more complex than that. This source code (and the compiled binaries) does not contain the PC-specific DOS code, which were supposed to be written by

It is even more complex than that. This source code (and the compiled binaries) does not contain the PC-specific DOS code, which were supposed to be written by the OEM (in PC case that probably means IBM). In order to build bootable DOS out of this you have to link SYSINIT.OBJ and SYSIMES.OBJ and your hardware interface code into binary (on PC the result of that is IBMIO.COM for PC-DOS and IO.SYS for MS-DOS for PC) and if you want to boot from floppy you also have to provide some kind of bootloader.