System information

5.1 Introduction
This chapter describes CP/M (release 2) system organization including the structure of memory
and system entry points. This section provides the information you need to write programs that
operate under CP/M and that use the peripheral and disk I/O facilities of the system.
CP/M is logically divided into four parts, called the Basic Input/Output System (BIOS), the Basic
Disk Operating System (BDOS), the Console Command Processor (CCP), and the Transient
Program Area (TPA). The BIOS is a hardware-dependent module that defines the exact low level
interface with a particular computer system that is necessary for peripheral device I/O. Although
a standard BIOS is supplied by Digital Research, explicit instructions are provided for field
reconfiguration of the BIOS to match nearly any hardware environment, see Section 6.
The BIOS and BDOS are logically combined into a single module with a common entry point
and referred to as the FDOS. The CCP is a distinct program that uses the FDOS to provide a
human-oriented interface with the information that is cataloged on the back-up storage device.
The TPA is an area of memory, not used by the FDOS and CCP, where various nonresident
operating system commands and user programs are executed. The lower portion of memory is
reserved for system information and is detailed in later sections. Memory organization of the
CP/M system is shown in Figure 5-1.
Section 5
CP/M 2 System Interface
5-1