DOS/32 Advanced DOS Extender - Programmer's Reference
3.04 - DOS function 1Ch - Get Specific Drive Info
AH = 1Ch DL = drive number
if successful: AL = sectors per cluster ECX = bytes per sector EDX = total number of clusters on drive DS:EBX = pointer to media ID byte
if failed: AL = 0FFh (invalid drive in DL)
a) The selector returned in DS register will be zero selector, ie readable/writeable data selector with Base=0. This is an internal to DOS/32 Advanced selector which may NOT be freed or modified under any circumstances.