[charcircuit]

I thought it started by executing microcode from ROM.

[martyvis]

Which is precisely what another of today's HN posts alludes to https://news.ycombinator.com/item?id=34329201

[valleyer]

It does, in the sense that executing any (regular, macro) code involves executing microcode. But no, there's not a separate phase during which only microcode is executed, if that's what you mean.