As far as intellectual property protections go, You wouldn't be able to copy the layout of an old AMD or Intel processor copyright infringement, not that anyone would want to, because it wouldn't be cost effective to use the exact same process decades later. There's no trademark protection, as AMD was unable to register the x86-64 trademark (https://tsdr.uspto.gov/#caseNumber=76032083)
replyOther than protections against industrial espionage, that exhausts all forms of intellectual property rights in the US.
The microcode is protected by copyright; see NEC Corporation v. Intel Corporation.
replyMicrocode is specific to a given implementation, so if you make your own x86 implementation, it's not going to run AMD's or Intel's microcode unless you go out of your way to make it do so. NEC didn't infringe Intel's copyright, because their processor ran different microcode than Intel's, and NEC won that lawsuit.
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