[chubot]

I imagine part of it is vertical integration. If you make the hardware that the CPU integrates with, and the OS that runs on the hardware, you can do a lot of optimization.

Intel CPUs don't know what memory they're talking to, i.e. they have to support a variety of memory. Likewise they don't necessarily know what OS they're running; how it context switches, etc. If it's virtualized, etc. Sure they have optimizations for those common cases, but the design is sort of accreted rather than derived from first principles.

To make an analogy, if you know your JS is running on v8, you can do a bunch of optimization so you don't fall off the cliff of the JIT, and get say 10x performance wins in many cases. But if you're writing JS abstractly then you may use different patterns that hit slow paths in different VMs. Performance is a leaky abstraction.