CP/M on the MZ-80A -
Disk Parameter Block & Bootstrap Code
written by Maurice Hawes / SUC/UK
Source: SUC-magazine July 2003, Volume 23 Number 2, p. 13
|Sharp Users Club - MZ-80A Section - CP/M via DPB.COM|
Parameters for Drive A:
( CP/M 18.104.22.168, like most CP/M systems, uses 128-byte logical sectors )
80 Sectors per Track seems impossibly high until you realize that, in M-T's CP/M 2.2 on the MZ-80A, a 'Logical Track' extends over BOTH sides of a disk and there are therefore only 35 'Logical Tracks' on the disk as a whole.
Each such 'Logical Track' has a capacity of 128 * 80 Bytes = 10,240
( 10K ), and the capacity of a whole disk is
BSH = 4 and BLM = 15 both give a block size of 2K ( 2048 bytes ).
EXM = 1 implies that, in this case, a 'Physical Extent' contains TWO 'Logical Extents' and is therefore 32K.
DSM = 169 implies that a disk contains 170 CP/M blocks ( i.e. 340K ).
DRM = 127 implies that the Directory can hold 128 entries.
AL0 - AL1 = 1100 0000 implies that the Directory is allocated the first 2 CP/M blocks ( i.e. Blocks 00 & 01, 4K ).
OFS = 1 implies that Track 0 is reserved for system use, and
that the first CP/M block ( Block 00 ) is at the start of Track 1.
The FILES.COM program in M-T's 5.25" MZ-80A CP/M confirms this figure.
DISCMOD3 reveals the following sections of code on Track 0:-
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