https://www.pcgamer.com/nvidia-adds-gddr5x-to-its-popular-gtx-1060-line/

Over the weekend, Nvidia quietly updated its pages on the GTX 1060 graphics card. Details are scarce right now, with the only major update being the line that says "6GB GDDR5/X"—specifically the slash-X bit at the end. As Tom's Hardware notes, there are already four variants of the GTX 1060 in the wild: the commonly known 1060 3GB and 1060 6GB, plus a 1060 6GB with higher clocked GDDR5 memory, and finally a quirky 1060 5GB model that's mostly seen overseas. The GDDR5X variant would boost memory bandwidth, and potentially offer better overall performance, though how much better remains to be seen.

Where things get interesting is speculation on how Nvidia adds GDDR5X into the mix. GDDR5 and GDDR5X are not pin compatible, despite the similar names. GDDR5 comes in a 170-ball BGA format, while GDDR5X uses 190-ball BGA. There are other differences as well, like quad-data-rate vs. double-data-rate, and prior to this point it was assumed that only the GP104 and GP102 GPUs from Nvidia had the ability to interface with GDDR5X. That leaves two possibilities.