Spinning disks under GMR heads are fundamentally a 2D technology. You might eke out a few more layers with a GMR array (like radar for magnetism), but there wil

Spinning disks under GMR heads are fundamentally a 2D technology. You might eke out a few more layers with a GMR array (like radar for magnetism), but there will be a noise limit. Flash technology will become stackable. Not just multi-bit per cell. The major limitation to NAND flash going to multiple layers is the inability to do epitaxy on deposited layers. The other approach is to use new materials that offer some form of hysteresis in amorphous or polycrystalline form, like 3D X-point. This product line was abandoned for business reasons, but I’m fairly confident that it will make a comeback in a big way, either by [insert big Asian company] buying the IP, or a well-funded startup. There’s also more exotic data storage like optical holography. That’s also 3D data storage, but with very little heat accumulation, which is the problem with anything based on 3D electronics. It is technically a spinning disk though.