Delete data on hard drives correctly
Before you hand over your computer or hard drives to third parties or for electronic waste recycling, you should delete the hard drives or physically destroy them.
Normal deletion does nothing
In Windows, files are usually moved to the so-called “recycle bin” when they are deleted – in reality, this corresponds to the trash under your desk. The data is not removed from this area until the wastebasket is full, ie the specified storage space is occupied or if the user himself empties the wastebasket. However, only the references to the data in the index, the table of contents of the hard disk, are deleted and the area is overwritten. This overwriting may never happen. The supposedly disposed data are still on the hard drive, but are no longer accessible to the user by normal means.
Even fully formatting a hard drive or a disk may not be able to completely erase data. With normal formatting, the so-called high-level formatting, only the file system structure is newly created; So the complete table of contents deleted and replaced by a new one. Again, the digital data is still on the disk. Formatting is therefore unsuitable as a secure deletion method.
Delete data correctly
However, the statement “delete data correctly” must be preceded by the fact that this applies only to data to which the overwriting program has access. Modern semiconductor-based storage media (SSD) and also the hard disks (HDD) or combinations (SSHD) working with magnetic media use very complicated mechanisms to control errors that occur. All methods have in common that they prevent access to defective memory areas of application programs, which also include all overwrite programs. Hard drives also allow the establishment of protected hard drive areas (HPA). With special analysis programs, however, these locked / protected memory areas may be readable as far as physically possible.
Data on intact hard disks can be erased completely and not recoverable with special software by overwriting. The data is overwritten one or more times with given characters or random numbers, which is sufficient in most cases. With older hard disks (<80GB) the data should be overwritten 7 times.
Modern hard disks allow the use of the ATA “Secure-Erase” command. In this case, a manufacturer-specific routine in the hard disk is triggered, which is to delete the entire hard disk including defective memory areas. For SSD or SSHD, this deletion method is recommended. The use of “Secure Erase” should be combined with the random numbers above. The volumes are still usable after overwriting.
In the software market, there are both freeware and commercial products that perform the mentioned overwriting methods. Most of these tools offer several methods of overwriting.
We recommend using programs to overwrite the hard drives, which are started from a bootable medium (e.g. CD, USB stick) and overwrite the hard drives as a whole. An example is the freeware Darik’s Boot And Nuke (DBAN) or Parted Magic . Parted-Magic enables overwriting using “Secure Erase” ; the edition “Parted Magic 2013-08-01” from August 2013 is available free of charge.
You can download the program DBAN on the pages of the magazine Computerbild , Parted-Magic is available at heise-online .
Note : We recommend that you overwrite hard drives that you distribute to trusted third parties, regardless of any operating system you have installed. Please note that if the hard disk is overwritten as a whole, it also overwrites recovery partitions of the manufacturer and the operating system.
This can be done, for example, with a bootable CD of the freeware Darik’s Boot And Nuke (DBAN) . The program can be downloaded computer screen on the pages of the magazine.
Here we provide instructions on how to use DBAN or Parted-Magic for overwriting hard drives. If the overwrite programs are working properly, ask a knowledgeable person for help.
If you do not want to overwrite a hard disk or if you cannot because of a defect, you should physically damage or destroy the hard disk. This also applies to storage media such as CD / DVDs or USB sticks.
If you have always wanted to see a hard drive from the inside, this would be the right time. Do maximum damage to the object. Be careful, however, and put on appropriate protective clothing.
Even the bending of the disks means that the common methods of data recovery are no longer applicable. Please note that some hard disk manufacturers have used glass panes and can break CDs or DVDs very violently. With SSD hard drives or USB sticks, you have to damage the individual memory chips.