: _err LIT" FDerr" ERR ;
: _cylsec ( sec -- cs, return sector/cylinder for given secid )
    ( 4 256b sectors per block, 10 sec per cyl, 40 cyl max )
    10 /MOD ( sec cyl )
    DUP 39 > IF _err THEN
    8 LSHIFT + ( cylsec )
;
: FD@! ( wref blk -- )
    1 @DCSTAT NOT IF _err THEN
    2 LSHIFT ( 4 * -- wr sec )
    4 0 DO ( wr sec )
        DUP I + _cylsec ( wr sec cs )
        I 8 LSHIFT BLK( + ( wr sec cs addr )
        1 ROT ROT ( wr sec drv cs addr )
        4 PICK EXECUTE NOT IF _err THEN
    LOOP 2DROP ;
