Wait, wasn't it more a part of their model than for Intel? We're talking about the era of mandatory access control and time sharing.

I mean, the 360/91 that he's talking about didn't even have an MMU.

Wait--weren't MMUs available back even on the 65/67?

Only the 67 for the 360s, and there the software hadn't really caught up. On the 370s it was more prevalent, but they had gone back to in order designs at that point.

I don't think this is really correct. From August 1965, multiprogramming was offered using DAT (Dynamic Address Translation)--what they called MMUs back then.

And this feature was used to support not only many programs running at once, but also TSO (Time Sharing Option) which by definition is mutually untrusted code.

TSO didn't depend on hardware boundaries between clients.