I would love if it's more modern - say a dedicated build of very stable Linux with heavy security - but on the other hand, older tech usually is simpler, and more reliable, easier to trouble spot or maintain.
They probably at least run it in a vm container or something on modern hardware, it's not impossible to migrate away from legacy systems, run it in a container, then replicate it in modern software with gradual rollout, then upgrade the software.
This would cause soo much chaos though, air traffic is one of those constants 24/7 jigsaw pieces so even doing a 3 day break would send shit in turmoil.