System information

Table 6-6. (continued)
Locations Contents
0040H-004FH A 16-byte area reserved for scratch by CBIOS, but is not used for any
purpose in the distribution version of CP/M.
0050H-005BH Not currently used; reserved.
005CH-007CH Default File Control Block produced for a transient program by the CCP.
007DH-007FH Optional default random record position.
0080H-00FFH Default 128-byte disk buffer, also filled with the command line when a
transient is loaded under the CCP.
This information is set up for normal operation under the CP/M system, but can be overwritten
by a transient program if the BDOS facilities are not required by the transient.
If, for example, a particular program performs only simple I/O and must begin execution at
location 0, it can first be loaded into the TPA, using normal CP/M facilities, with a small
memory move program that gets control when loaded. The memory move program must get
control from location 0100H, which is the assumed beginning of all transient programs. The
move program can then proceed to the entire memory image down to location 0 and pass control
to the starting address of the memory load.
If the BIOS is overwritten or if location 0, containing the warm start entry point, is overwritten,
the operator must bring the CP/M system back into memory with a cold start sequence.
6.9 Reserved Locations in Page Zero CP/M Operating System Manual
6-27