I've encountered some newer systems running FreeDOS, which includes controllers, HMIs and along with some vendor-provided USB boot tools. In time these will be

I've encountered some newer systems running FreeDOS, which includes controllers, HMIs and along with some vendor-provided USB boot tools. In time these will become legacy systems. In new deployments these non-PLC industrial systems are some combination of CE, XP, or very rarely 7. Linux is starting to gain traction with some Rockwell touch panels, but your typical vendor is loathe to try anything new. If software innovation were left to the industrial vendors, we'd still be on parchment and punch cards.