Altirium Data Recovery Blog

“How many layers of data can you go down on a hard disk drive?” was the question over the phone. Not really a silly question, there is so much mis-information about how hard it is to erase data from hard drives, and how “data-can-be-recovered-even-after-the-platters-have-melted” (possibly the latter is a slight exaggeration).

It is worth debunking the myth quickly. With a hard disk there is a single layer of recordable material on each side of each platter. When an area of this disk is written to, whatever was at the area previously has gone forever. No need to write over it seven times, no need to sandblast the disk.

If a hard disk drive is re-formatted and then new data written to it, some or all of the original data will be written over and will never be found, there is no hard drive data recovery technique that will get it back.

So, why does data keep turning up where it shouldn’t? Medical records on hard disks in computers that have been sold on etc.? Just as when military laptops are left in cars or on trains, this is not a technical issue, just shear carelessness. With the exception of a few sectors that are mapped out by a hard drive’s defect management system there is nothing to stop all data being eradicated from any hard disk, and however much Brasso is used you can’t polish through to any older data.

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