I used to work on Stratus servers, and I think the company was purchased by IBM in the late 90s.
For each running component in the system, there are three physical instances. They use a voting system to drop any disagreement in RAM or the outcome of an instruction. In the 3 years I dealt with them, I never saw a system failure, and the only outages were caused by planned system upgrades. OS stuff. All of the hardware was hit swapped.
These were multimillion dollar machines that basically had the CPU performance of a couple of 68000 CPUs.
I personally witnessed a take out of a Novell 2.x file server which had a 16 year uptime. This was for a school system, and they had forgotten where the file server was. Stuffed in the back of a janitorial closet, and dust covered. That wasn't any sort of fancy hardware.m, but an old microchannel PC.
If you don't need to patch them, computers run for a long time.