Demerits

Each stage of parallel operation requires time measured in hours & days with extensive human and mechanical intervention between steps.DNA systems are very error prone and messy because it takes some time to extract the final answer from DNA pool formed during computations and DNA strands breakup with time. So the chance of error increases. One of the drawbacks is that so far no one has found a problem that is suitable for DNA computers which means so far no killer application has been found for DNA computers. As remarked by David Harlanwood,”DNA Computing is a solution looking for problem”.
But on the other other hand DNA2DNA computations13 could be regarded as the killer application which involves the use of DNA computing to perform operations on unknown pieces of DNA without having to sequence them first. This could be achieved by recoding and amplifying unknown strands into a redundant form so that the can be operated. Many of the errors that could be seen in other DNA models could be ignored here because of such a high availability of numbers for operation. Another demerit is that the test tube environment used for DNA computing cannot be considered as the practical use. And DNA solution13 looks like water if seen by the naked eye so output is not visible like conventional computers.