Very interesting that mainframes were really only "dead" for about 10-15 years or so: [0] from the early/mid 90's to EC2 in 2006. Yes, the cloud if off-site, but I'm using mainframe in the sense of centralized non-desktop computing resources.

[0] Not that they were ever actually dead. There's mainframes around from decades ago, and HPC continued to be required for a variety of applications, specifically research. But in terms of day-to-day computation needs, things shifted from mainframes to desktops, and centralized systems tended to be servers dedicated to a specific purpose instead of general compute needs.