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Fun fact: the AMD64 patents have expired, with AMD-V patents expiring this year, so there really isn't a need for an x86 license to do anything useful. All that's still protected is various AVX instruction sets, but those are generally used in heavily optimized software, like emulators and video encoders, that tend to be compiled to the specific processor instruction set anyway.
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As far as I can remember, it is not only a "patent" issue. It seems there are other legal mechanisms.

That said, I would not use a x86_64 CPU without AVX nowadays.

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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)

Other than protections against industrial espionage, that exhausts all forms of intellectual property rights in the US.

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The microcode is protected by copyright; see NEC Corporation v. Intel Corporation.
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Microcode 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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How could we given you keep bringing it up whether it’s relevant or not?
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