The Ryzen 9 3900X redefines our expectations for the mainstream desktop with 12 cores and 24 threads for roughly the same price as Intel’s eight-core Core i9-9900K. The extra cores deliver big gains in heavily threaded applications, and the improved architecture offers great gaming performance, too, making for an incredibly well-rounded processor. Support for the PCIe 4.0 interface is the cherry on top.
Read more @ Tom’s Hardware
Starting at the top we have the Ryzen 3900X, which is a 12-core design. In fact it’s the first 12-core processor in a standard desktop socket, and it rather unique within AMD’s product stack because it is currently the only SKU which takes full advantage of AMD’s newest chiplet architecture. Whereas all the other Ryzen parts are comprised of two chiplets – the base I/O die and a single CPU chiplet – 3900X comes with two such CPU chiplets, granting it (some of) the extra cores and the 64MB of L3 cache that entails.
Read more @ AnandTech