System information

removable cartridge disk, or fixed hard disk. Hard disk capacities range from five to several
hundred megabytes of storage.
diskdef macro library: Library of code that when used with MAC, the Digital Research macro
assembler, creates disk definition tables such as the DPB and DPH automatically.
disk drive: Peripheral device that reads and writes information on disk. CP/M assigns a letter to
each drive under its control. For example, CP/M may refer to the drives in a four-drive system as
A, B, C, and D.
disk parameter block (DPB): Data structure referenced by one or more disk parameter headers.
The disk parameter block defines disk characteristics in the fields listed below:
SPT is the total number of sectors per track.
BSH is the data allocation block shift factor.
BLM is the data allocation block mask.
EXM is the extent mask determined by BLS and DSM.
DSM is the maximum data block number.
DRM is the maximum number of directory entries-1.
AL0 reserves directory blocks.
AL1 reserves directory blocks.
CKS is the number of directory sectors check summed.
OFF is the number of reserved system tracks.
The address of the disk parameter block is located in the disk parameter header at DPbase +
0AH. CP/M Function 31 returns the DPB address. Drives with the same characteristics can use
the same disk parameter header, and thus the same DPB. However, drives with different
characteristics must each have their own disk parameter header and disk parameter blocks. When
the BDOS calls the SELDSK entry point in the BIOS, SELDSK must return the address of the
drive's disk parameter header in register HL.
disk parameter header (DPH): Data structure that contains information about the disk drive
and provides a scratchpad area for certain BDOS operations. The disk parameter header contains
six bytes of scratchpad area for the BDOS, and the following five 2-byte parameters:
XLT is the sector translation table address.
DIRBUF is the directory buffer address.
DPB is the disk parameter block address.
CSV is the checksum vector address.
ALV is the allocation vector address.
Given n disk drives, the disk parameter headers are arranged in a table whose first row of 16
bytes corresponds to drive 0, with the last row corresponding to drive n - 1.
DKS: Parameter in the diskdef macro library specifying the number of data blocks on the drive.
Appendix H : Glossary CP/M Operating System Manual
H-8