If you were using Emacs before and now started using Vim & vi, then this mistake is commited very often and will be quite annoying to you.

You hit "control x" "control s" to save the file and Vim stops dead. How to rescue without killing the xwindow containing the vim process, and recovering. You will see that there is no response at the keyboard.

The explanation for this behaviour is : It is not the feature of vim but it is the feature of the xterm 'terminal'. The "control s" means stop feeding to terminal output, so you do not see any output. To get out of it do "control q" (to quit out of stop output). This happens only in vim/vi and not in gvim (graphical Vim).

Also in xterm, at the bash prompt type something and do "control s" and type something you will not see output. Now type "control q" you will see output.