Gave examples of what features old ones had in the essay below with the first link mentioning the specific systems for further inspection:
https://www.schneier.com/blog/archives/2014/04/dan_geer_on_h...
Note: B5500, System/38, and Ten15/FLEX are all especially worth considering. Two were basically HLL machines with type-safety and interface safety enforced at hardware level. System/38 was object-based with HW- and SW-level protections plus portable microcode layer.
I'd say Channel I/O counts as one that kicks modern systems' asses. Servers have been copying it bit by bit over past ten years, maybe even exceeding it, but server OS's are inherently inferior in usage given mainframe OS's are designed for I/O offloading at core. Near interrupt-less architecture with acceleration engines makes many apps scream with performance. And would only cost $10 per CPU on desktops but would require Windows & Linux rewrites. (sighs)
However, the change to the AS/400 and POWER cost it one of its greatest features: hardware-enforced integrity at the object level. That's the feature that would still be giving hackers hell if it was widely deployed. The Intel i432 APX and i960MX had similar property. Interesting enough, IBM actually has secure CPU's they've prototyped and even sold to select customers. Would be great if they integrated one with IBM i at microcode, compiler, and OS levels. That plus an optional interface for new customers without legacy crap would be a huge differentiator that might give it new life.
Close enough... I grew up on XTs, i286, i386, so on :) All of them way weaker than my phone (Not sure if that was what you were referring to).
However, in terms of architecture, algorithms, programming language features... It feels like we haven't advanced too much. Actually, the opposite... we are encourage now to do not be too clever on programming because processing power and memory usage is close to be a commodity and clean code is more important (which is fine but less fun).