[yodon]

Agreed, and most people don't realize that this stuff almost "can't" be upgraded because the initial vendor back in the late 80's or early 90's specified a specific tech stack in the contract and any upgrading or even application of OS patches would legimitately violate any warranties and liabilities the original vendor has for their work. This is super time-critical physical process code commonly running on operating systems like Win95 or Win3.1 that were never intended to be real time operating systems and whose behavior could change radically if a patch were installed.

The cost and complexity of designing and tuning the process control software, and the lack of the detailed design calculations involved in figuring out what it needed to be written to do 20 or 30 years ago makes replacing that old tech stack nearly equivalent to replacing the entire installation.

Big power plants, refineries, and chemical plants truly are the worst of all legacy nightmares.