User`s guide

Figure 1-5. System Components and Regions in Logical Memory
The Basic Input/Output System, BIOS, is a hardware-dependent module that defines
the low-level interface to a particular computer system. It contains the device-driving
routines necessary for peripheral device I/O.
The Basic Disk Operating System, BDOS, is the hardware-independent module that
is the logical nucleus of CP/M 3. It provides a standard operating environment for
transient programs by making services available through numbered system function
calls.
The LOADER module handles program loading for the Console Command Proces-
sor and transient programs. Usually, this module is not resident when transient pro-
grams execute. However, when it is resident, transient programs can access this
module by making BDOS Function 59 calls.
Resident System Extensions, RSXS, are temporary additional operating system
modules that can selectively extend or modify normal operating system functions.
The LOADER module is always resident when RSXs are active.
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1.2 System Components CP/M 3 Programmer's Guide