I think "looks like" is very ephemeral to what being a mainframe IS. it's true that MP systems can look like a single entity, but they are highly asynchronous. The prism architecture meant a single clock state propagating cleanly across the CPU(s) provided a consistent, time managed framework to be all things to all people. (thats how I understand it)<p>A Sun E10000 is to my mind, as close as a mainframe gets in the post-sparc era. The Tandem non-stops had some of it, the final Dec cluster model was getting there but in a distributed async clocked manner.<p>In the end the point of the mainframe was the TPC. The sustained rate it could process edge device request-response sequences inside the bounds of your choices in the CAP theorem. Distributed systems solve the same problem, but with other consequences. It still freaks me out that IBM had so many irons in the fire they had room to do this, AND to make unix work inside this, and manage legacy, and scale out to whole-of-government or SAGE or SABRE or you-name-it.<p>I hated using AIX as a sysadmin from Dec world view btw. I'm not an IBM fanboi. I lived in the competition.