Considering the strangeness of this question, perhaps you should explain what it is you are attempting to accomplish. Why are you wanting to erase all of the ram on a running system?

True on the cold boot issue. One with physical access to any system could much more easily attack it.

As to what could be removed from a normal power off (say 10 minutes) from a system would be somewhat unknown. I'd suspect going to a full power off with ac removed would help secure it more.

The question is inadequate. All the guessing is interesting.

On military systems they worry about this very thing. RAM that has held the secret code can be read after power off by grinding down the wafer and probing with an ion beam. There have been several proposed solutions to defeat this. It would be another assumption that the original poster was or was not worried about this level of exposure.

For purposes of donating or recycling a computer, power off would be adequate for the RAM, but not for the hard drive, as has been noted.

If it has held sensitive information, then a power cycle with any other bootable binary would adequately invalidate any residual RAM charges for most purposes. A standalone memtest program has been used for this purpose.

Hard drives are also hard to entirely invalidate. The dd solution would get the obvious readable data, but given sufficient importance, examining residual patterns in the magnetic disk layer can reveal most of the original information. Some organizations use a drill through the hard drive. I have heard that some military use a commercial shredder on their hard drives.

Short of nuking the site from orbit**, the only way to be sure...

(** with hat tip to Ellen Ripley)

@selfprogrammed
I take it your post was purely academic (although interesting). If the OP had access to such techniques, or his data has to be sucured against such techniques, he would not be posting this question in LQ.

And in case he is in a position where this is relevant and he did post here, he is totally unsuitable for the job.

jlinkels

I like ion beams.

I like nukes. It is the only way to be sure man.

In the absence of atomic bombs a handfull of rust and alumin[i]um, a piece of magnesium and a gas flame ought to do it.