IBM 3270 Manual page 103

We will show you how to arrange them to look
like this:
Follow these instructions even if you don't have
the same number of windows. After you do the
first two you will know enough to do the rest on
your own.
Changing the Size of the First Window
Let's place the first window in the upper left
corner of your screen:
1. If your work station is not in Control Mode,
press the WSCtrl key.
This line should appear at the bottom of your
screen:
WSCTRL
WINDOW=C SCREEN=O
9-6 Book 3 - Using the Control Program