[rayiner]

There is a little more complexity that bears on why companies like Intel would have their own fab. In practice, a processor design isn’t just a circuit diagram (or a netlist: https://en.m.wikipedia.org/wiki/Netlist). A circuit diagram is an idealized model that hardware does not totally reflect. For example, wires have capacitance and transistors leak current. In fact the smaller the process node, the less the real circuits reflect idealized circuits. High-performance designs thus are tuned for the specific properties of the process.

Historically, Intel has not only led in process technology, but has reaped benefits from having the process engineers next door to the processor designers. Intel CPUs have been tuned for the exact process that will be used to make them, including by laying out transistors by hand to maximize performance.

Custom design happens with foundaries as well, of course, but there have historically been synergies from putting processor design and process design under the same roof.

[dnautics]

I have heard the argument? Rumors? that Intel has suffered from the closeness of the chip designers to the process engineers... for a long time if the process is not robust, the designers could workaround, but that made it hard for non-in-house designers to develop. The need for robustness has forced a discipline in the tsmc process engineers to be more disciplined, which scales well downward.