Every single physical core on the chip decodes and executes both s390x and Arm AArch64 instructions, dynamically switching between the two ISA modes and convert them into micro ops. Mode switching is hypervisor-driven.
And those chips are fast. 5.7 Ghz 2nm node.
For who: When you need to run Linux programs on high security, mission critical environment. Others should not care.
https://www.servethehome.com/ibm-z-and-linuxone-dual-isa-pro...
Why couldn't they be 6GHz? x86_64 ISA did it again?
That said IBM should add RISC-V support.
So I guess the IBM stuff is "server slow" then.
I wish RISC-V microarchitectures would get access to 2nm silicon processes, because RISC-V at 7GHz... yummy.
So, don't assume they would crank up the GHz.
I have to admit we were more in the "desktop" use case, then the 7GHz (I don't know how they will manage to keep the backend reasonably fed without severe speculation though).