INT 21 - DOS 1+ - NULL FUNCTION FOR CP/M COMPATIBILITY
AH = 18h
Return: AL = 00h
Note:   corresponds to the CP/M BDOS function "get bit map of logged drives",
which is meaningless under MSDOS
SeeAlso: AH=1Eh,AH=20h,AX=4459h

See also: 211D

2118 - DOS 1+ - NULL FUNCTION FOR CP/M COMPATIBILITY