The device is an upgrade of a similar machine that the scientists made about a year ago, which used ATP molecules as an energy source.

In this version of the automaton, DNA molecules serve as input, output and software. The restriction enzyme FokI serves as the hardware, aiding the cleavage of the input DNA molecule. It's this cleavage that releases the energy to drive the device. The input data molecule is destroyed in the reaction, while the software and hardware molecules remain unchanged.

According to the researchers, a fixed amount of software and hardware molecules can, in principle, process any input molecule of any length without external energy supply.

What's more, the ATP-free device works better than its ATP-consuming predecessor. Under optimum conditions, the device performed calculations at an initial rate of 20 seconds per step per input molecule - about 50 times faster than the previous system. The device also had a parallel processing performance about 8000 times better, conducting 6.646 x 1010 operations per second per ml.

The scientists say that a 5 ml spoonful of "computer soup" could contain 15,000 trillion of the devices, in total performing 330 trillion operations per second, with 99.9% accuracy per step. The computers would together release less than 25 µWatts in heat.

The scientists reported their work in the Proceedings of the National Academy of Sciences USA.