Chapter 7
BIOS Disk Definition Tables
CP/M-86,
like
CP/M-80,
is
a table-driven operating system with a separate field-
configurable Basic
I/O
System (BIOS).
By
altering specific subroutines in the BIOS
presented in the previous chapters,
NEC
has customized
CP/M-86
for operation
on
the APC.
The purpose
of
this
chapter
is
to
present the organization
and
construction
of
tables
within the BIOS
that
define the characteristics
of
the disk system used with
CP/M-
86. The
APC
is configured to operate with single-sided, single-density
(lD)
and
double-sided, double density (2D) diskettes,
and
with
hard
disks.
DISK PARAMETER TABLE FORMAT
In
general, each disk drive has
an
associated 16-byte disk
parameter
header
which
contains
information
about
the disk drive
and
also provides a
scratchpad
area for
certain BDOS operations. The
format
of
the disk
parameter
header for each drive
is
shown below.
Disk Parameter Header
XLT
0000 0000
0000
DIRBUF
DPB
CSV ALV
16b
16b 16b 16b 16b 16b 16b 16b
Each element is a
word
(16-bit) value. The meaning
of
each Disk Parameter
Header
(DPH)
element
is
given in Table 7-1.
7-1
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