DRAM. However, since the "cells" in a hard drive are much smaller, the storage density for hard drives is much higher than DRAM. Hard drives are ''non-volatile'' -- data is retained even after power is removed.

Millipede storage attempts to combine features of both. Like a hard drive, millipede both stores data in a medium and accesses the data by moving the medium under the head. Also similar to hard drives, millipede's physical medium stores a bit in a small area, leading to high storage