> from IBM banning the use of their mainframe OSes in emulation It doesn't change your point (which is that it appears de facto legally established that IBM ca

> from IBM banning the use of their mainframe OSes in emulation It doesn't change your point (which is that it appears de facto legally established that IBM can do this), but IBM doesn't completely ban the use of their mainframe OSes in emulation. They are totally okay with people running them in their own emulators (zPDT and ZDT); the thing they won't authorise is people running them on the open source Hercules emulator, since their own emulators cost $$$$, and Hercules is free, and it appears they view the $0 of Hercules as a threat to the $$$$ of their mainframe ecosystem. In the past they've even authorised third party commercial emulators, such as FLEX-ES. At some point they stopped allowing FLEX-ES for new customers, although I believe some customers who bought licenses when it was allowed are still licensed to use it. But, it isn't impossible they might authorise a third party commercial emulator again – make it expensive, non-open source, and make it only run on IBM hardware (such as POWER Systems), and there's a chance IBM might go along with it.