How does this software work??

 >> What is the difference between that and Fast400 from IBM's perspective?

I would say the difference is very significant - certainly in a legal sense.
One is using documented features of the OS, the other is the result of
reverse engineering the OS.  Since reverse engineering the OS contravenes
the OS/400 license, then for sure the person who wrote the tool (and I
suspect those who sell it) are in contravention.  Not sure if IBM's license
terms make it illegal to utilize such knowledge, but it wouldn't surprise me
knowing IBM's lawyers.

Seems to me though that all IBM has to do to stop this from working is to
add a test or two of this bit to the workstation data management code, and
simply error out if the bit is not set.  That can't be that hard to do can
it?  If they take that approach then you are down to patching code to make
the thing work again and now you are certainly contravening you OS/400
license.

I suspect that IBM will block this but may not do so until after they have
taken some action to provide a better pricing model for 5250 use.

Jon Paris
Partner400