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BIOS Disk Definition Tables
Returning to the DPH description, note that the two address values CSVand ALV
remain. Both addresses reference an area of uninitialized memory following the
BIOS. The areas must be unique for each drive. The size of each area is determined
by the values in the DPB.
The size of the area addressed by CSV is CKS bytes, which is sufficient to hold the
directory check information for a drive. If CKS
=
(DRM+I)/4, (DRM+I)/4 bytes
must be reserved for directory check use. If CKS is 0, no storage is reserved.
The size of the area addressed by ALV is determined by the maximum number of
data blocks allowed for a particular disk, and is computed as (DSM/8)+ 1.
Table 7-7 lists the DPS values for single-density diskettes, double-density diskettes,
and hard disks for the APC.
Table 7-7
DPB
Values For The
APe
FD-1D
FD-2D
HARD DISK
SPT
26
52
64
BSH
3
4
6
BLM
7
15
63
EXM
0
0
3
DSM
242
493
562
256 x 26 x 8 x 86.5
(
-1 )
8192
DRM
63
255
511
ALO
192
240
192
ALl
0
0
0
CKS
16
64
0
OFF
2
2
0
7-7
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