On 4/9/2013 7:37 AM, Steve Richter wrote:
but why? because of the design of the workstation controller, no? A 5250
data stream could be stateless in that all the information needed to
reestatblish state is contained in the data sent down to the device.
Why? I'd say because stateful terminal connections were the prevailing
way of doing things when 5250 was designed. It involves writing text to
the display, defining where the fields are, and then sitting and waiting
for a response from the terminal.
The OS can, at any point during the wait, lock the keyboard, erase the
screen and bring up another screen. For example, when a break message
arrives, it cancels "invite" ("locks keyboard") from the terminal, and
instructs the terminal to save the original screen, and bring up a new
one. This requires a stateful connection. (We work around this in our
Genie product by waiting for the next time the user submits the screen,
and then putting up the break message -- but it doesn't quite work the
A similar situation arises when you "time-out" the display of a screen.
So, ultimately, in order to make it stateless, you'd have to change the
way 5250 works, at least a little bit. Then, you'd have to replace all
the existing 5250 clients (Client Access, Rumba, QuestView, TN5250J,
etc, not to mention actual terminals) with new stateless software. If
you're going to go through all of that, why not just use an established,
mainstream protocol like HTTP?
I could make a case there is a need even now to expand the display and
interaction capabilities of what is displayed on a 5250 display screen. But
the focus of my questions are more on what happened 10-15 years ago when
IBM was still adding significant software capabilities to the system. Why
did they stop?
Because, after 40 or so years, 5250 had reached the end of it's life of
enhancements. It just didn't make sense to keep enhancing something
that's so old and out of date with what people want to do.
If you had reworked the workstation controller couldn't an
interactive job have become more or less web like? Images would be able to
be displayed, direct links to other 5250 display programs, change the font,
start adding client side code.
Sure... but it makes a whole lot more sense to integrate with the web
browsers that everyone uses rather than try to make PC5250 be
"web-like". Every new device that comes out today has a browser built
in to it. Mobile phones, tablets, etc are the tip of the iceberg. My
Sony PSP has a browser. My Nintendo Wii has a browser. All of these
"automatically" work with http... but good luck convincing them to work
with 5250, even if you add web capabilities to it.
It just makes more sense to use the modern HTTP protocol rather than