In two dimensions, if you assume one base per square nanometer, the data density is over one million Gbits per square inch. Another important property of DNA is its double stranded nature. The bases A and T, and C and G, can bind together, forming base pairs . Therefore every DNA sequence has a natural complement. This complementarity makes DNA a unique data structure for computation and can be exploited in many ways.
Error correction is one example.
Errors in DNA happen due to many factors. Occasionally, DNA enzymes simply make mistakes, cutting where they shouldn't, or inserting a T for a G. DNA can also be damaged by thermal energy and UV energy from the sun. If the error occurs in one of the strands of double stranded DNA, repair enzymes can restore the proper DNA sequence by using the complement strand as a reference. In this sense, double stranded DNA is similar to a RAID 1 array , where data is mirrored on two drives, allowing data to be recovered from the second drive if errors occur on the first. In biological systems, this facility for error correction means that the error rate can be quite low.