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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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