Determines if the specified drive is associated with a path and, if it is, retrieves the associated path.
mov ax, 71aah ; SUBST
mov bh, 2 ; Query SUBST
mov bl, DriveNum ; see below
mov dx, seg PathName ; see below
mov ds, dx
mov dx, offset PathName
int 21h
jc error
Clears the carry flag and retrieves the associated path in the specified buffer if successful. Otherwise, the function sets the carry flag and returns an error value in the AX register.