Basic
I/O
System (BIOS) Functions
5-2
ORGANIZATION
OF
THE
BIOS
The
BIOS
portion
of
CP
IM-86
resides in the topmost
part
of
the operating system
(highest addresses),
and
takes the general form shown in Figure 5-2.
CS,
DS,
ES, SS:
Console
Command
Processor
and
Basic
Disk
Operating
System
CS
+ 2500H:
BIOS
Jump
Vector
CS + 253FH:
BIOS Entry Points
BIOS:
Disk
Parameter
Tables
U nini tialized
Scratch
RAM
Figure 5-2 General CP/M-86 Organization
In
order
to
implement CP
IM-86
on
the
APC
hardware,
NEC
has modified the
standard
BIOS distributed by Digital Research, Inc.
to
create a BIOS which
performs the functions listed in
Chapters
5
and
6.
The cold
start
loader
that
loads
the
CPM.syS
into memory contains a simplified form
of
the BIOS, called the
LDBIOS
(Loader
BIOS).
It
loads CPM.SYS into memory
at
the location defined in
the
CPM.SYS header (absolute address 0400H).
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