为什么要覆盖文件多次以安全地删除文件的所有痕迹？ [英] Why overwrite a file more than once to securely delete all traces of a file?

问题描述

诸如Eraser之类的擦除程序建议覆盖数据36次。

Erasing programs such as Eraser recommend overwriting data maybe 36 times.

据我了解，所有数据都以1或0的形式存储在硬盘中。

As I understand it all data is stored on a hard drive as 1s or 0s.

如果对整个文件执行一次随机的1和0覆盖，那为什么还不足以删除原始文件的所有痕迹？

If an overwrite of random 1s and 0s is carried out once over the whole file then why isn't that enough to remove all traces of the original file?

推荐答案

曾经是0，然后变为 1的硬盘位，其磁场强度比以前使用的弱。变为1，然后再次写入1。使用敏感的设备，通过测量强度的细微差异，可以以合理的准确度识别出每个位的先前内容。结果将不完全正确，并且会出现错误，但是可以检索到以前的内容中的很大一部分。

A hard drive bit which used to be a 0, and is then changed to a '1', has a slightly weaker magnetic field than one which used to be a 1 and was then written to 1 again. With sensitive equipment the previous contents of each bit can be discerned with a reasonable degree of accuracy, by measuring the slight variances in strength. The result won't be exactly correct and there will be errors, but a good portion of the previous contents can be retrieved.

位35次，实际上是不可能分辨过去的。

By the time you've scribbled over the bits 35 times, it is effectively impossible to discern what used to be there.

编辑： 现代分析显示，单个被覆盖的位可以恢复率仅为56％。尝试恢复整个字节的准确时间仅为0.97％。所以我只是在重复一个城市传奇。使用软盘或其他介质时可能需要多次重写，但是硬盘不需要。

A modern analysis shows that a single overwritten bit can be recovered with only 56% accuracy. Trying to recover an entire byte is only accurate 0.97% of the time. So I was just repeating an urban legend. Overwriting multiple times might have been necessary when working with floppy disks or some other medium, but hard disks do not need it.

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