IBM 3270 Manual page 41

3. If DOS is running in that session, look for the
DOS ready message:
Or:
4. Or, if a PC program is running in that
session, look for the information or messages
that the program normally puts on the screen.
You are now ready to begin using your PC
session. Each PC session looks and works as if it
were an IBM Personal Computer. You may have
DOS running or you may have a Personal
Computer program running.
At any time, you can use the Jump key to go to
another session.
4-2 Book 3 - Using the Control Program