Same with industrial automation. There’s some robotic arms, assembly lines, etc in use today that still use PCs with ISA slots - the predecessor to PCI, which was the predecessor to PCIe. Old 16-bit bus with a max speed of around 5Mbps. That’s why you’ll occasionally see newish “industrial” motherboards that have ISA slots and parallel ports.

They also often have a lot of the hardware in stock and ready to deploy, to handle replacements.

A project I worked on at university (way back in 2010) was for one of the largest providers of air traffic control systems. Our project was interesting - overlaying eye tracking data from Tobii eye trackers they provided (thousands of dollars each at the time) on top of screen recordings taken via VNC, to aid in training of air traffic controllers.

It was even more interesting to learn about some of their processes, though. Whenever they built an ATC computer system for a client, they’d build one or two spares at the same time, with exactly identical hardware. They did this for two reasons:

1. If the hardware breaks down, they can supply a new system that exactly matches the hardware that was verified.
2. If a client has an issue with their system, they can try and replicate the issue on a clone of that client’s system.

We got to see a storage room with a large number of these systems. Lots of different PCs anywhere from a month to maybe 15 years old. :)