System information

6.10 Disk Parameter Tables
Tables are included in the BIOS that describe the particular characteristics of the disk subsystem
used with CP/M. These tables can be either hand-coded, as shown in the sample CBIOS in
Appendix B, or automatically generated using the DISKDEF macro library, as shown in
Appendix F. The purpose here is to describe the elements of these tables.
In general, each disk drive has an associated (16-byte) disk parameter header that contains
information about the disk drive and provides a scratch pad area for certain BDOS operations.
The format of the disk parameter header for each drive is shown in Figure 6-2, where each
element is a word (16-bit) value.
DISK PARAMETER HEADER
+-------+------+------+------+----------+-------+-------+-------+
| XLT | 0000 | 0000 | 0000 |DIRBUF| DPB | CSV | ALV |
+------+------+------+-------+----------+-------+-------+-------+
16B 16B 16B 16B 16B 16B 16B 16B
Figure 6-2. Disk Parameter Header Format
The meaning of each Disk Parameter Header (DPH) element is detailed in Table 6-7.
Table 6-7. Disk Parameter Headers
Disk Parameter
Header Meaning
XLTAddress of the logical-to-physical translation vector, if used for this particular drive, or
the value 0000H if no sector translation takes place (that is, the physical and logical sector
numbers are the same). Disk drives with identical sector skew factors share the same translate
tables.
0000 Scratch pad values for use within the BDOS, initial value is unimportant.
DIRBUF Address of a 128-byte scratch pad area for directory operations within
BDOS. All DPHs address the same scratch pad area.
6.9 Reserved Locations in Page Zero CP/M Operating System Manual
6-28