User`s guide

Figure 1-6. System Modules and Regions in Logical Memory
First note that all memory regions in CP/M 3 are page-aligned. This means that
regions and operating system modules must begin on a page boundary. A page is
defined as 256 bytes, so a page boundary always begins at an address where the low-
order byte is zero.
The term High Memory in Figure 1-6 denotes the high address of a CP/M 3
system. This address may fall below the actual top of memory address if space above
the operating system has been allocated for directory hashing or data buffering by
GENCPM. The maximum top of memory address for both banked and nonbanked
systems is 64K-1 (OFFFFH).
T'he labels BIOS-base, BDOS_base, and LOADER_base represent the base addresses
of the operating system regions. These addresses always fall on page boundaries. The
size of the BIOS region is not fixed, but is determined by the requirements of the
host computer system.
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1.3 Component Interaction CP/M 3 Programmer's Guide