First, they are the first CPU designers to finally admit that the age of designing instruction sets is over.
CPU designers solved a similar problem by using multiple parallel cores.
CPU designers sometimes incorporate one or more undocumented machine code instructions for testing purposes.
Do those elite teams of CPU designers simply not resemble typical application developers?
CPU designers therefore tried to make instructions that would do as much work as feasible.
So many CPU designers choose a PLRU algorithm which only needs one bit per cache item to work.
Reportedly, it allowed the CPU designers to achieve a higher degree of parallelism, by using an auxiliary execution unit for the address registers.
A CPU designer is often required to implement a particular instruction set, and so cannot change N.
In the 1960s memory was relatively expensive, and CPU designers produced instruction sets that densely encoded instructions and data in order to better utilize this resource.
I recall, back around '95, attending lectures by some of the top CPU designers of the time.