Here is a question that came in from Quora:
Unlike ASICs and CPUs, the closer you cram together the 1s and 0s in a storage device, the less reliable it gets. Taking the question at face value, the TLC technology in a 480 MicroSD card (something like this one) is already crammed together as close as it can possibly get. And with the sizes that you’re talking about, you’ll need more than 2000x the number of cells in the same space for each cell to get that kind of density.
Worse, because the cells are so crammed together for the bits, they don’t last very long (about 300–500 overwrites). This is a really bad idea for a hard drive used for long-term storage.
Technology for high density storage is moving in different directions – the most obvious is “vertical.” Levant Peckan’s answer about the current 100TB drive is a very good example of this. Samsung’s 3D NAND and Intel’s Optane drives are examples of a matrix-style approach that uses vertical layers and strata to achieve the densities while reducing the trade-offs and sacrifices one has to make in order to achieve those goals.
But SD cards (and MicroSD cards) do not use that technology. They are designed for fast(ish) and cheap – but not good. You only get 2 out of the three, and with long-term storage you need good and fast, but not necessarily cheap.