Windows XP checking in, and I know of at least one other lab still using 2000 (for, IIRC, a thermogravimetric analysis machine). The problem is drivers: Lots of very spendy equipment (test, measurement, fabrication, etc) needs a host PC to run, and often needs a specific OS version because the manufacturer decided to EOL the product.

It is not unusual for a $50 OS upgrade to necessitate hundreds of thousands of dollars of software and hardware upgrades. So we just don't upgrade the OS.

Looks like XP is the 2nd most common variant of Windows according to this page on Wikipedia[1]. I'm sure there are ways to criticize/pick apart the different sampling techniques used, but none have XP above 7 anymore. Certainly not a non-trivial amount of XP machines out there though.

[1] https://en.wikipedia.org/wiki/Operating_system_usage_share