Creating new CP/M disk from scratch

Now, for the tough part. You need to write a CBIOS, which at a minimum, has your terminal I/O routines and disk I/O routines. The terminal I/O is going to depend on what hardware you have. The simplest is using a connection to a serial terminal. More complex routines may be needed if what you have is a video-mapped display. The disk routines aren't too bad. One set of them simply passes the disk parameter block information to CP/M; the other entry points merely store the track and sector and unit and transfer address of what's to be read or written and then reads or writes it. Part of the CBIOS is also the cold boot loader, which loads the DOS part of CP/M. There are other useful features in the CBIOS, such as punch, printer, and reader I/O as well as IOBYTE redirection, but you can do those later.

Peruse the "CP/M System Alteration Guide" for examples of how to build a CBIOS and a boot loader.