  The properties and fundamental limits of chemical computers have recently
attracted significant interest as a model of computation, an unifying principle
of cellular organisation and in the context of bio-engineering. As of yet,
research in this topic is based on case-studies. There exists no generally
accepted criterion to distinguish between chemical processes that compute and
those that do not. Here, the concept of entropy driven computer (EDC) is
proposed as a general model of chemical computation. It is found that entropy
driven computation is subject to a trade-off between accuracy and entropy
production, but unlike many biological systems, there are no trade-offs
involving time. The latter only arise when it is taken into account that the
observation of the state of the EDC is not energy neutral, but comes at a cost.
The significance of this conclusion in relation to biological systems is
discussed. Three examples of biological computers, including an implementation
of a neural network as an EDC are given.
