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Many additions and extensions have been added to the x86 instruction set over the years, almost consistently with full backward compatibility. The architecture has been implemented in processors from Intel, Cyrix, AMD, VIA Technologies and many other companies; there are also open implementations, such as the Zet SoC platform (currently inactive). Nevertheless, of those, only Intel, AMD, VIA Technologies, and DM&amp;P Electronics hold x86 architectural licenses, and from these, only the first two are actively producing modern 64-bit designs.