Der8auer purchased a retail Threadripper 1950X and found what appears to be four active Zeppelin die soldered to the IHS. We followed up with AMD for more detail.
Earlier this year, Der8auer delidded a Threadripper engineering sample and found that the processors still feature all four Zeppelin die, similar to AMD's EPYC data center processors. AMD uses only two die for the Threadripper models, so many speculated that it might be possible to unlock the other dies and their extra cores.
AMD responded that two of the die on shipping Threadripper models are not the same as those Der8auer found in the engineering sample--the additional two die are "dummy" die that the company uses to provide structural stability for the package. These additional die prevent the IHS (Integrated Heat Spreader) from caving in when you tighten down the heatsink.
Recently, Der8auer followed up and purchased a retail Threadripper 1950X, then created a custom delidder to remove the IHS. Again, he found four Zeppelin die soldered to the IHS but decided to take his experiment further and determine if the additional packages were "real" die or just inserts. Der8auer removed the die by placing the processor onto a heated copper block (300C), thus weakening the bonds from the PCB. After removing the packages, he used a diamond lapping material to expose the die.
Der8auer found that all four die appear to be "real" die (you can clearly see the two four-core complexes). We followed up with AMD and inquired if the die were functional. AMD responded that two of the die are in fact non-functional "dummy" die that aren't connected electrically to the substrate.
During AMD's Hotchips presentation, the company outlined Threadripper's MCM package and indicated that each die features four Infinity Fabric links, but the company uses only three links for the EPYC processors. This technique minimizes trace length to reduce latency. Because the company doesn't electrically connect two of the Threadripper die to the substrate, it's natural to assume that the company is using only two Infinity Fabric links for the two active dies. That also scuttles any chances of activating the two "extra" die.
Mounting dies to a substrate is like any other manufacturing process; there can be defects. It's possible that the Threadripper processors are simply EPYC processors with die that weren't successfully mated to the substrate. Conversely, it's also possible that AMD is using defective die for the fillers, but in either case, it's doubtful that the company is wasting functioning silicon. We've followed up with AMD for additional clarification and will update as necessary. In the meantime, we suggest watching the video for an interesting look inside the die removal process.