* BIOS (Basic Input/Output System): It consists of input/output routines. It manages data transfer between the CPU and various peripherals.
* BDOS (Basic Disk Operating System): It directs the activities of the disk controller and manages the file allocation on the disk. It allocates memory space under a file name.
* CCP (Console Command Processor): It handles your input from the "A>" prompt.
The CCP and BDOS are machine independent and are made by Digital Research. The BIOS is implemented by the vendor (e.g. Amstrad).
There are other CP/M compatible systems or systems that replace part of CPM CP/M to fix bugs and enhance it:
* [[Z80DOS]]
* [[Z-System]]