title: When I write a file in mode "wb", what will happens?
body: <p>When I write "asklfj123" into a file in mode "wb", then I open it in vim,
  why I can still see  asklfj ?but I can not see 123 in vim. I mean that when I write it in mode "wb", the program will not convert it into ASCII code, but the editor will open it with ASCII code, then it should be garbage values in text editor, isn't it? then why I can still see them?  </p>