In an interview with Overclockers UK, AMD’s James Prior mentioned that its second-generation Ryzen desktop processors will support the existing AM4 socket: current Ryzen platform users will be able to seamlessly upgrade to the new processors with a BIOS update. The company plans to keep AM4 its mainstream-desktop processor socket until 2020, which means at least another two to three generations of processors for it.
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Source: [H]ardOCP – AMD Second-Generation Ryzen “Pinnacle Ridge” Confirmed to Support AM4