A single pass is enough to destroy any data on the drive for all practical purposes.

The myth that overwritten data can be recovered comes from a study one researcher did that used a clean drive, wrote data to it, then overwrote all the data with zeros. He then examined the bit patterns on the platter and was in some cases, able to determine whether that bit had been 1 or 0 before the wipe. However, this method requires dis-assembling the drive and examining the platter with equipment that costs at the very least, tens of thousand of dollars. Not only that, but doing so is extremely time consuming. Add to that the fact that if the particular section of the drive you’re looking at was ever written to more than once during normal use, it will be virtually impossible to determine the previous state of that bit.

In other words, you have to own a hugely expensive piece of equipment, take the drive apart, spend days or even months studying each individual bit and in the end, you may have recovered enough bits to spell out a single word.

Without taking the drive apart, you’re not going to be able to recover anything. Hard drives are designed to write one and only one copy of data to any given sector of the drive. When you ask the drive to read that sector back to you, it can only read the most recently written data. There is no secret command that tells the drive to tell you what was there before it was overwritten.

Don’t believe me? Format your drive, and I mean a FULL format, not just a quick erase. Then call up every data recovery service you can find, tell them that you performed a full or “low level” format on the drive and ask how much they’d charge to recover all your data. Make sure that you stress that the data was only overwritten ONCE. They’ll tell you that it’s imposisble.

If it does, George W. Harper will probably do all he can to help — the US.

Cheers!

Some end users I can see not knowing how to do that, but companies should never trust another company with their sensitive information.