IBM 3270 Manual page 137

3. If you are not sure of the number of the
screen profile, press the PFI key.
A list of the screens that are in use will
appear at the right side of the screen. The
screens with no windows listed are not being
used.
For example,
SCRN:WINOOWS WINDOWS
O:ABCD APC1
1:A
2:BC
3:DCA
4:
5:
6:
7:
8:
9:
B:HOST1
C:NOHPAD1
D:NOTEPAD2
9-40 Book 3 - Using the Control Program