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How can i wipe RAM completeley before or during the shutdown process of Windows 7?

I tried several programs and a script but later i noticed that all those options only claim to free unused RAM space.

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    Isn't the wipe of RAM coming from shutdown enough for you? Its not completely wiped out, but reading needs expensive equipment. – user10008 Aug 21 '14 at 2:18
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    Turn the computer off and wait 15 seconds? – Fiasco Labs Aug 21 '14 at 3:59
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DDR memory technology has to be "refreshed" continuously by the memory controller in order to prevent the data from decaying into an unreliable state. Essentially, each "cell" of memory is a small capacitor which can be charged or not charged (representing 0 or 1). When you power down, the memory is no longer being refreshed, so that charge leaks out. The data gets less and less coherent over time, until it's just garbage.

If you're using DDR3, the maximum time you'll need to wait for data coherence to reduce to the 50% mark at room temperature (~25C) after power-off is about 45 seconds, though in practice it can be as short as 1.5 seconds. Once memory reaches this point, there is statistically no way to know whether its original value was a 0 or a 1 - it is unrecoverable. Keep in mind that the rate of loss of coherence is proportionate to temperature, so if your memory is a fair bit hotter than ~25C (it probably will be) then it'll likely lose coherence much faster. Equally, if you run your memory at below-freezing temperatures (hardcore overclocker, perhaps?) then the rate of coherence loss will be slower.

So, to answer your question more directly, you don't need to do anything but sit there for a minute after you've powered off. Unless your threat model includes someone grabbing your laptop and dumping it into a convenient bucket of liquid nitrogen during the first couple of seconds after power-off, you'll be fine.

  • "(hardcore overclocker, perhaps?)" Or the FBI ;) – Luc Aug 21 '14 at 13:59
  • @Luc I'd be more worried about DMA memory dump when an attacker gains access to a running computer. – CodesInChaos Aug 22 '14 at 9:29

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