Current disk densities are about 10^12 bits&#x2F;square inch. To get 800 terabits on a single platter, it would need a diameter of about 32 inches. At 10^14 bits&#x2F;square inch, only 3.2 inches.<p>Assuming a compound annual growth rate of 25%, densities will be 10-fold larger in 10 years, and 100-fold larger in 20 years. (This actually happened in hard disks between 1972 and 1992.) But that would take us to 2035, not 2020.<p>At those densities, a bit will have to be stored inside a square about 7 or 8 nanometers on a side. I don&#x27;t know whether that&#x27;s possible.