Scientists have successfully turned DNA rewritable memory. Stanford researcher Drew Endy and his team have, using elements from a bacteriophage, built and demonstrated a rewritable recombinase addressable data (RAD) module. The system consists of a stretch of DNA flanked by sites that signal to enzymes made by the bacteriophage, instructing them to cut out the DNA and paste it back into the chromosome in the reverse orientation. The DNA can be set and reset repeatedly — up to 16 times. The device is digital, with forward and reverse orientations of the DNA acting like a ’0′ or a ’1′ in binary. Endy sees the device tracking cellular events, for example, counting the number of cell divisions it takes for a stem cell to become a differentiated adult cell, like a cell in the liver. Building the system wasn’t easy, though. It took over 750 different designs to get the device working. Hopefully, future designs will take less debugging.