Before you give your computer or hard drives to a third party or for electronic waste recycling, you should erase or physically destroy the hard drives.
Emptying the recycling bin is useless
Under Windows, in most cases, files are first moved to the so-called “Recycle Bin” when they are deleted – in reality, this corresponds to the Recycle Bin under your desk. The data is only removed from this area when the Recycle Bin is full, i.e. when the specified storage space is occupied, or when the user empties the Recycle Bin himself. However, only the references to the data in the index, the table of contents of the hard disk, are deleted and the area is released for overwriting. However, this overwriting may never take place. The supposedly discarded data is still on the hard disk, but is no longer accessible to the user by normal means.
Even the complete formatting of a hard disk or a data carrier may not be able to delete data completely. With normal formatting, the so-called high-level formatting, only the file system structure is newly created; that is, the complete table of contents is deleted and replaced by a new one. Here, too, the digital data are still on the data medium. 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 only applies to data to which the overwriting program has access. Modern semiconductor-based storage media (SSD) and also the hard disks (HDD) or combinations of hard disks (SSHD) working with magnetic media use very complicated mechanisms to control any errors that occur. Common to all methods is that they prevent access to defective memory areas of application programs, including all overwrite programs. Hard disks also allow the creation of protected hard disk areas (HPA). With special analysis programs, however, these locked/protected memory areas can be read out if necessary, as far as this is still physically possible.
Data on intact hard disks can be completely and irretrievably deleted by overwriting with special software. In doing so, the data is overwritten once or several times with predefined characters or random numbers, which is sufficient in most cases. With older hard disks (< 80GB) the data should be overwritten 7 times.
Modern hard drives allow the use of the ATA “Secure-Erase” command. This triggers a manufacturer-specific routine in the hard disk, which should erase the entire hard disk including defective memory areas. This erase method is recommended for SSD or SSHD. The use of Secure Erase should be combined with the random number overwriting mentioned above. The media will still be usable after overwriting.
If you are not sure how to proceed or if the overwriting programs are working properly, ask a competent person for assistance.
If you do not want to overwrite a hard disk or cannot do so due to 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 the inside of a hard disk, this would be the right time. Do maximum damage to the object. However, be careful and put on appropriate protective clothing.
Even bending the panes means that the usual methods of data recovery are no longer applicable. Please note that some hard disk manufacturers have used glass panes and CDs or DVDs can shatter very violently. With SSD hard disks or USB sticks you must actually destroy the individual memory chips.