Most of those old POS systems were actually either 3270 or (more likely) 5250 applications; i.e., block mode terminals instead of character mode terminals. Whil

Most of those old POS systems were actually either 3270 or (more likely) 5250 applications; i.e., block mode terminals instead of character mode terminals. While the difference between block mode and character mode terminals is a fundamental technical difference, that difference impacts the UI in two major ways: 1) Most interaction is local, and therefore quick. All of the editing, jumping between fields, and even basic validation happened on the terminal itself. It was only when you submitted your changes or loaded a new screen that the server would even get involved (much like a web form without Javascript); therefore, even in an installation with a lot of active terminals, these green screen applications would be incredibly responsive. 2) Every screen and application had exactly the same user interface. Even function keys were mostly standardized (ever wonder where F1=Help came from?), so what you learned in one place in the UI would trivially generalize to everywhere else in the UI.