https://mastodon.social/@nixCraft/111839478303640635
It's also worth noting that the original mainframe hardware has likely been virtualized at this point. Used to work for a company that was doing a lot of that around 15 years ago
The as400 is a mini-computer, the high end of this line overlaps the low end of mainframe.
When I did some consulting work out there many years ago, they had a network of the largest as400's that IBM makes, connected together in one image.
Regarding virtualization: It would have to be on IBM's power processors. IBM does offer cloud services running as400, I have no info on whether Costco is using that or not.