  Molecular data systems have the potential to store information at
dramatically higher density than existing electronic media. Some of the first
experimental demonstrations of this idea have used DNA, but nature also uses a
wide diversity of smaller non-polymeric molecules to preserve, process, and
transmit information. In this paper, we present a general framework for
quantifying chemical memory, which is not limited to polymers and extends to
mixtures of molecules of all types. We show that the theoretical limit for
molecular information is two orders of magnitude denser by mass than DNA,
although this comes with different practical constraints on total capacity. We
experimentally demonstrate kilobyte-scale information storage in mixtures of
small synthetic molecules, and we consider some of the new perspectives that
will be necessary to harness the information capacity available from the vast
non-genomic chemical space.
