collapseos/arch/8086/pcat/blk/607

: _ ( AX BX sec )
    ( AH=read sectors, AL=1 sector, BX=dest,
      CH=trackno CL=secno DH=head DL=drive )
    FDSPT C@ /MOD ( AX BX sec trk )
    FDHEADS C@ /MOD ( AX BX sec head trk )
    8 LSHIFT ROT OR 1+ ( AX BX head CX )
    SWAP 8 LSHIFT 0x03 C@ ( boot drive ) OR ( AX BX CX DX )
    13H 2DROP 2DROP
;