UNDOCUMENTED CP/M FUNCTIONS cont. From Microsystems, May 1983, p.70 CP/M issues a dummy call to the BIOS 'HOME' routine prior to a directory read. Early versions of the 'CP/M 2.2 Alteration Guide' did not include the following sentence in the description of the SELDSK function of the BIOS: The least significant bit of register E is zero if this is the first occurrence of the drive select since the last cold or warm start. This information can provide a clue to the BIOS that it may need to log-in a disk that has been changed.