Memory Materials on One Budget: The Physics of Retention Media Compared

Six retention media (DRAM, NAND flash, magnetic disk and tape, phase-change memory, FeRAM, and MRAM) are compared on a single physical budget: retention mechanism, physical failure channel, characteristic energy barrier from the literature, retention time at 300 K computed by anchored Arrhenius scaling, and holding energy per bit-year computed from published device figures. DRAM is the only medium with second-scale retention and a large continuous holding cost (1.38e-4 J per bit-year); every nonvolatile medium retains unpowered at zero holding energy, with computed 300 K retention from 1.52 years (end-of-life NAND flash) to 9.88e7 years (phase-change memory). Magnetic tape on a shelf is cheapest per bit-year at scale; phase-change memory is most stable per joule. Model calculations are simulated, not measured. Computations and drafting were performed with Dave, an AI research system.