I have installed quite a few PLCs, yet I have never had to replace a hard drive. For a very obvious reason.
Neither have I ever had to worry about providing air-conditioning or an extremely clean power supply.
All the systems were up and running form complete shutdown in a matter of a few seconds and could take a complete abrupt power loss without a squeak. A maintenance technician was able to troubleshoot the problems and even do some code changes - with me just being on the phone and saving myself the travails of travel.
The moral is simple: a PC controlling a machine is an abomination. Some limited use as a secondary device (vision... maybe, data collection & analysis, fancy operator interface). Too flimsy, too slow, too unreliable (no matter Windows or Linux or whatever).
Sorry though, I am sure this topic has been raised a lot of times here...