For those not familiar with the 3270 terminals they're actually kind of interesting and very different from more familiar character-cell terminals. I found this out doing the "master the mainframe" contest years back - it's like a whole other world. Each screen has a set of editable regions (with formatting) and the terminal provides a line editor for those regions, and a way to submit the whole screen's edits to the mainframe. That way a user can fill out a whole form without the computer receiving any interrupts at all.