Comment by zdragnar

I don't really know the full details, as it was my brother who worked there and we just chatted over beers, but I believe the software itself that communicated over the parallel ports was 16 bit, and that (along with the native ports) was the reason they kept the old windows XP machines around.

It is possible, perhaps almost a certainly, that the company did not own the source code for the application and could or would not attempt to rewrite it to work with a modern operating system.

This is a top brand name company, so it isn't like they couldn't throw money at the problem, but with the number of lines in the number of plants they had, there wasn't really any reason to not keep the old hardware running (sans Internet connection).