Display based editing is the focus of vi .
If you have used ed you will find that, in addition to hav- ing all of the ed commands available, ex has a number of additional features useful on CRT terminals. Intelligent terminals and high speed terminals are very pleasant to use with vi . The ex utility contains a number of features for easily viewing the text of the file. The z command gives easy access to windows of text. Of course, the screen-oriented visual mode gives constant access to editing context.