System information

The entry points into the BIOS from the cold start loader and BDOS are detailed below. Entry to
the BIOS is through a jump vector located at 4A00H + b, as shown below. See Appendixes A
and B. The jump vector is a sequence of 17 jump instructions that send program control to the
individual BIOS subroutines. The BIOS subroutines might be empty for certain functions (they
might contain a single RET operation) during reconfiguration of CP/M, but the entries must be
present in the jump vector.
The jump vector at 4A00H + b takes the form shown below, where the individual jump addresses
are given to the left:
4A00H+b JMP BOOT ;ARRIVE HERE FROM COLD START LOAD
4A03H+b JMP WBOOT ;ARRIVE HERE FOR WARM START
4A06H+b JMP CONST ;CHECK FOR CONSOLE CHAR READY
Table 6-3. CP/M Disk Sector Allocation
Track Sector Page # Memory Address CP/M Module name
' 16 20 4800H + b
' 17 ' 4880H + b
' 18 21 4900H + b
01 19 ' 4980H + b BDOS
07 20 22 4A00H + b BIOS
' 21 ' 4A80H + b
' 22 23 4B00H + b
' 23 ' 4B80H + b
' 24 24 4C00H + b
01 25 ' 4C80H + b BIOS
01 26 25 4D00H + b BIOS
02-76 01-26 (directory and data)
6.6 The BIOS Entry Points
6.5 Disk Organization CP/M Operating System Manual
6-15