Like the 7950X3D and 7900X3D, these new X3D chips combine a pair of AMD’s CPU chiplets, one that has the extra 64MB of cache stacked underneath it and one that doesn’t. For the 7950X3D, you get eight cores with extra cache and eight without; for the 7900X3D, you get eight cores with extra cache and four without.
It’s up to AMD’s chipset software to decide what kinds of apps get to run on each kind of CPU core. Non-gaming workloads prioritize the normal CPU cores, which are generally capable of slightly higher peak clock speeds, while games that benefit disproportionately from the extra cache are run on those cores instead. AMD’s software can “park” the non-V-Cache CPU cores when you’re playing games to ensure they’re not accidentally being run on less-suitable CPU cores.
We didn’t have issues with this core parking technology when we initially tested the 7950X3D and 7900X3D, and AMD has steadily made improvements since then to make sure that core parking is working properly. The new 9000-series X3D chips should benefit from that work, too. To get the best results, AMD officially recommends a fresh and fully updated Windows install, along with the newest BIOS for your motherboard and the newest AMD chipset drivers; swapping out another Ryzen CPU for an X3D model (or vice versa) without reinstalling Windows can occasionally lead to CPUs being parked (or not parked) when they are supposed to be (or not supposed to be).