Screen Size and Model Guide¶
3270 screen size depends on the terminal model in use.
Model Sizes¶
| Model | Rows | Columns | Typical use |
|---|---|---|---|
| 2 | 24 | 80 | Standard 3270 screens |
| 3 | 32 | 80 | Extra rows |
| 4 | 43 | 80 | Large-screen workflows |
| 5 | 27 | 132 | Wide-screen workflows |
Why This Matters¶
Your model affects:
- How much of a screen is visible
- Cursor coordinates used in recordings
- Compatibility with host applications that expect a specific size
If a host app expects 24x80, use Model 2 unless instructed otherwise.
Choosing a Model¶
Set your model in configuration or .env.
Example:
S3270_MODEL=2
Alternative values are also accepted (for example 3279-4-E).
Larger Than the Model: Oversize Displays¶
A model decides the standard screen size, and a display can be configured
larger than that one. The setting is S3270_OVERSIZE — "Oversize" under
Display Behavior in Settings — written as columns by rows:
S3270_MODEL=2
S3270_OVERSIZE=100x30
Two things are worth knowing before switching it on.
The host has to ask for it. An oversize display starts at its model's standard size and switches to the larger one only when an application writes to the alternate screen. Until then a 100x30 display is a 24x80 one, and the status bar says so. That is the architecture rather than a limitation: an application that was written for 24x80 gets 24x80.
The application has to want it. Most host applications draw a fixed panel and will paint their 24 rows into the top of a taller screen, leaving the rest blank. Oversize earns its keep where the application is one that adapts — a browser or an editor that fills whatever it is given.
AS/400 and IBM i Hosts¶
These hosts drive their terminals with 5250, not 3270, and 3270Web does not
speak 5250 — neither does the s3270 it runs. What makes them reachable is a
front end on the host that translates between the two protocols. It works, and
it comes with two conditions worth knowing before the first connection rather
than after it.
Use model 2. An AS/400 or IBM i host does not natively understand any 3270 model other than model 2, at 24x80. This is not the usual "unless the application wants otherwise" advice that applies elsewhere on this page: any other model is simply the wrong answer against these hosts.
S3270_MODEL=2
Expect 5250 function keys to arrive as PF-key sequences. The front end
expresses 5250-specific operations through 3270 keys, so a key the host
documentation names once may be two keystrokes here. 5250 Clear is PF3, and
5250 F3 is PA1 followed by PF3. Recordings store the 3270 keys actually sent —
that F3 is saved as PressPA1 then PressPF3 — so a session captured against
one of these hosts replays without any 5250 knowledge on 3270Web's part.
Both conditions are properties of the host's front end rather than of 3270Web,
and they are documented upstream by the x3270 project whose s3270 3270Web
drives: 5250 support. Native
5250 sits on the feature roadmap.
Practical Guidance¶
- When recordings fail at
FillStringcoordinates, confirm the same model is active — and the same oversize setting, which changes the coordinates as surely as the model does. - Keep the same model across environments (dev/test/prod) for reliable playback.
- If text alignment looks wrong, check both model and code page settings.
- Against an AS/400 or IBM i host, use model 2 — see above.