[Function declarations]
   FUNCTION ulong GetLogicalDrives() LIBRARY "Kernel32.dll"
   FUNCTION uint GetDriveType( Ref String as_root_path ) 
     LIBRARY "kernel32.dll" ALIAS FOR "GetDriveTypeA"

   [PB function]

   integer   li_ctr
   string    ls_root
   ulong     lul_drives, lul_rem

   lul_drives = GetLogicalDrives()

   DO
     lul_rem = MOD(lul_drives, 2)
     IF lul_rem = 1 THEN
        ls_root = Char(li_ctr + 64) + ":\"
        IF GetDriveType(ls_root_path) = 5 THEN
           Return ls_root_path
        END IF
        li_ctr ++
     END IF
     lul_drives /= 2
   LOOP UNTIL lul_drives = 0

   RETURN ""