function GetHDCode(Drv: string): string;

var

  VolumeSerialNumber: DWORD;

  MaximumComponentLength: DWORD;

  FileSystemFlags: DWORD;

begin

  if Drv[Length(Drv)] = ':' then

    Drv := Drv + '\';

  GetVolumeInformation(Pchar(Drv), nil, 0, @VolumeSerialNumber, MaximumComponentLength, FileSystemFlags, nil, 0);

  Result := IntToStr(VolumeSerialNumber);

end;

procedure TForm1.FormCreate(Sender: TObject);

begin

memo1.Lines.Add(GetHDCode('c:'));

end;