Zero page (CP/M)

The Zero Page (or Base Page) is a data structure used in CP/M systems for programs to communicate with the operating system. In 8-bit CP/M versions it is located in the first 256 bytes of memory, hence its name.

The equivalent structure in DOS is the Program Segment Prefix (PSP), a 256-byte structure, which, however, is by default located at offset 0 in the program's load segment (rather than in segment 0) immediately preceding a loaded program.

In 8-bit CP/M, it has the following structure:

In CP/M-86, the structure is: