They did indeed mention 500TB. That doesn't mean they have actually stored 500TB anywhere, or that they have a system that's currently capable of storing 500TB

They did indeed mention 500TB. That doesn't mean they have actually stored 500TB anywhere, or that they have a system that's currently capable of storing 500TB anywhere, or even that they genuinely have good reason to think that their system can practically be made to store 500TB in something the size of a Blu-Ray disc. Maybe it can! But so far as I can tell the 10000x figure is much more what they hope might be achievable than what they are in any position to do. I don't have access to their actual paper. But the reports in the popular press seem to indicate that the individual voxels are on the order of 500x50nm in size, compared with Blu-Ray pits which are about 500x500nm. So that's a density increase of 10x within each layer. Each voxel apparently stores 4 bits, compared with one bit for a Blu-Ray pit, so that's a density increase of 40x. So if they're claiming 10000x, I think most of that increase has to be from having many many layers. They'd need 250 layers. So far they have done 3. It seems to me that the technical challenges in increasing the number of layers so greatly without reducing the density of voxels might be very great, because to read or write a voxel you need to point a laser at it, and as the number of layers increases they start getting in one another's way. Maybe they already have some ingenious solution to that problem -- again, I don't have access to their actual article. But I tend to think that if they'd solved that problem then (1) they would be making sure that the articles in the popular press tell the world of that achievement and (2) they would have demonstrated it with more than 3 layers. [EDITED to add:] Oh, wait, at least one of their publications is available to read: https://www.osapublishing.org/optica/fulltext.cfm?uri=optica-8-11-1365&id=462661 https://www.osapublishing.org/optica/fulltext.cfm?uri=optica... This one talks about "50 layers", though I'm not 100% sure whether they mean 50 full two-dimensional layers stacked on top of one another (their diagrams seem to suggest not), and says that with the parameters they used the amount they could fit on one disc would be ... 1.64TB. That's a ~30x increase over a dual-layer Blu-ray disc. Not to be sneezed at, for sure, but it's a lot less than 10000x. That paper is entitled "High speed ultrafast laser anisotropic nanostructuring by energy deposition control via near-field enhancement". It seems there's another one called "5D optical data storage with 100% readout accuracy in silica glass". Same authors, approximately same publication date, so it seems a bit unlikely that one of them is claiming 300x denser data storage than the other, but who knows?