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Video overview

Full-size WMV [211 MB]

A brief, accessible

introduction to our results

Memory remanence

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Full-size WMV [230 MB]

This video illustrates how an image stored in memory gradually decays over the course of 5 minutes after the computer is turned off.

Images

We loaded an image into memory, then cut power for varying lengths of time. After 5 seconds (left), the image is indistinguishable from the original. It becomes gradually more degraded, as shown after 30 seconds, 60 seconds, and 5 minutes. The horizontal bars result from the design of this memory chip, which represents some “1″ bits by the presence of charge and some by the absence of charge.

Ph.D. student Will Clarkson experiments with memory in Princeton’s computer science department.
By spraying an upside-down canister of multi-purpose duster directly onto the computer’s memory chips, we can cool them to -50 °C, greatly slowing the rate at which data decays.
In the upside-down position, the duster spray discharges very cold liquid refrigerant instead of gas.
A combination of frost and refrigerant around the computer’s memory chips. At this temperature, memory contents last for several minutes with almost no loss of information.
If we cool the memory and keep it cold, the information stored there will last for several minutes, even if we remove the memory from the computer.
Ph.D. student Nadia Heninger holds a container of liquid nitrogen. Liquid nitrogen boils at -196 °C; we used it to test the limits of cooling memory to low temperatures.
We stored data in these memory modules, then cooled them, removed them from the computer, and placed them in a container of liquid nitrogen for an hour. After returning them to the computer, we found practically no information had been lost. (Using liquid nitrogen would be overkill for most attacks, since cheap, widely-available duster spray would adequately cool the chips.)
Coauthors Seth Schoen and Jacob Appelbaum celebrate after the team submitted the paper for peer review.