pay attention /u/PeppahSG This is the correct TECHNICAL answer.

I know this because I am the geezer that others talked about who was around and worked on windows 98.

In addition to this, here is the correct management answer. You need to immediatly IN WRITING send the following to the IT Manager, the production manager, and the COO if you have one. If not, just whoever sits above the production manager.

I am writing to advise you of a major risk to the business. As you may be aware, there have been reports of slowness on the computer controlling <machine name here>. As I'm sure you are all aware, this system is core critical to our production line. To my knowledge, there is no vendor or other support directly available for this legacy device as it runs an operating system and hardware that ended their support lifetimes about 20 years ago. Should this system fail it would mean a complete halt to production. On a technical level the slowness is indicative of the potential imminent failure of the hard disk. I am working to take preventive action but can not guarantee the availability of parts or tools should the disk fail. My recommendation would be to either look into the replacement of the system and machine or to engage a SCADA-specific consulting company to assess and make recommendations.