Remanent magnetization myth or truth?

Question

Hard disks

Is it possible to recover data after a complete overwrite by residual magnetization? If this is a myth, then why does shred overwrite the file 25 times by default instead of once? If you know the answer, it is advisable to indicate the source.

Answer 1

35 times is the US standard for secure data erasing. In those days when storage volumes were small, data was recorded much less densely than now, the ability to measure the residual magnetization and determine something from it was much higher.

Answer 2

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