TSO, ISPF and the terminal
TSO is your interactive session on z/OS — a command line, essentially. ISPF is the full-screen menu system that runs on top of it, and it is where you will spend your day. The 'green screen' is a terminal emulator on your PC pretending to be a 3270 display.
Why the screen behaves oddly at first
A 3270 terminal does not send keystrokes as you type. It fills in a whole screen locally and sends it when you press an Attention Identifier key — Enter, or a function key. This explains almost every 'why did nothing happen' moment for newcomers: the mainframe genuinely has not heard from you yet.
- Enter is the primary send key — not a newline.
- PF3 is 'end / go back'. You will press it thousands of times.
- PF1 is help, PF7/PF8 page up and down, PF10/PF11 scroll left and right.
- Clear and Reset unlock a frozen keyboard. If typing does nothing and an X appears on the status line, press Reset.
- Fields you can type into are highlighted; everything else is protected.
The status line at the bottom
The bottom line of a 3270 screen shows the connection state and any input inhibit. X ( ) or a crossed symbol means the keyboard is locked — either the host is thinking, or you typed somewhere you are not allowed. Reset clears the second case.
------------------------- TSO/E LOGON ----------------------------- Userid ===> VSAHA1 Password ===> ******** Procedure ===> ISPFPROC Acct Nmbr ===> ACCT01 Then, at the READY prompt: READY ISPF
Common mistakes
Everything you type is discarded. Look at the status line, press Reset, then retype.
Use LOGOFF. Orphaned sessions are a common cause of 'I cannot log on' the next morning.
There isn't one. What left the screen is gone unless the application can page back with PF7.
What you will see at work
- Your site will standardise on one emulator; learn its keyboard mapping early, especially where it puts Reset and PF keys.
- Sessions time out. Losing an unsaved edit to a timeout happens to everyone once.
- Many sites now offer a web or IDE-based front end. The concepts on this page still apply underneath it.
Key terms
Check your understanding.
Take this lesson's quiz and save your progress. Free.