I can't really impose any hard definition, but I was wondering what the oldest server is that's still running on either the original hardware or original software. I don't mind if the software has a minor patch or two to fix bugs or security issues, or hardware has had parts replaced, but no major upgrade to newer hardware or newer versions of software. There are plenty of DNS servers that were set up in the 1980s and still run on the original domain name, but don't run the original software or hardware. So those wouldn't really count. I guess I'm wondering what software or hardware was sufficiently reliable that it didn't need upgrading over all those years (at least for a limited workload).
I update my machine all the time with new versions...