NEC CP/M-86 - Disk Parameter Block Fields

BIOS Disk Definition Tables
7-4
The translation vectors (XLT 00 through XL Tn-I) are located elsewhere in the
BIOS, and simply correspond one-far-one with the logical sector numbers zero
through the sector count minus one. The Disk Parameter Block (DPB) for each
drive is
more complex. ~A1 particular DPB, which is addressed by one or more DPHs,
takes the following general form.
SPT I BSH I BLM I EXM I DSM I DRM I ALO I ALl I CKS I OFF
16b 8b 8b 8b 16b 16b 8b 8b 16b 16b
Each field is a byte or word value, as shown by the "8b" or "16b" indicator below the
field. The fields are defined in Table 7-3.
Table 7-3 Disk Parameter Block Fields
FIELD
DEFINITION
SPT
Total number of sectors per track
BSH
Data allocation block shift factor, determined by the data
block allocation size
BLM
Block mask, determined by the data block allocation size
EXM
Extent mask, determined by the data block allocation size
and the number of disk blocks
DSM
Used to determine the total storage capacity of the disk
drive
DRM Used to determine the total number of directory entries
which
can be stored on the drive
ALO,ALI Used to determine reserved directory blocks
CKS
Size of the directory check vector
OFF
Number of reserved tracks at the beginning of the (logical)
disk