Am I right to assume that NAND flash has higher storage density than magnetic disks? I've been trying to find some definitive data about this but failed so far. I'd really appreciate if someone can point me the right direction to search.
http://ieeexplore.ieee.org/xpl/articleDetails.jsp?arnumber=6...
In 2012 they list the density of magnetic disks as 750 Gb/in^2 and nand flash as 550 Gb/in^2. I'm not sure how the numbers have changed with 2d nand, but 3d nand probably pushes the density way over magnetic.
MicroSD is 15x11x1 (165 mm^3), max size 200G
MicroSD is less than 0.5% the volume of 2.5" HDD, but 5% of the capacity. So MicroSD is an order of magnitude more dense than 2.5" HDD.
MicroSD still has to fit a little controller in there, so the comparison isn't particularly fair on flash. I expect heat management to be a problem scaling up though, apart from any manufacturing difficulties.