Mainframes tend to have prodigious amounts of expensive, unusually fast, specialised RAM. And then they have extremely smart controller hardware that the OSes can hand off almost everything off to.
And this is a theme replicated throughout mainframe design. Everything is replicated, all pathways are wide as possible, everything is integrated from the hardware up to the application layer.
Take virtualisation, for instance. IBM mainframes have PR/SM, a hardware-level capability to virtualise everything in the system down to the lowest level of granularity. And they've done this since 1985.
And this is a theme replicated throughout mainframe design. Everything is replicated, all pathways are wide as possible, everything is integrated from the hardware up to the application layer.
Take virtualisation, for instance. IBM mainframes have PR/SM, a hardware-level capability to virtualise everything in the system down to the lowest level of granularity. And they've done this since 1985.