Answer Description

When data is deleted or a disk is formatted the location of the data is tagged as empty and available for use but is not actually physically removed from the disk. This means after deleting it is still possible to read the data. Overwriting is a method that deletes the data and overwrites the physical location with random information to ensure it can never be recovered.

Wikipedia

Data erasure (sometimes referred to as data clearing, data wiping, or data destruction) is a software-based method of overwriting the data that aims to completely destroy all electronic data residing on a hard disk drive or other digital media by using zeros and ones to overwrite data onto all sectors of the device in an irreversible process. By overwriting the data on the storage device, the data is rendered irrecoverable and achieves data sanitization. Ideally, software designed for data erasure should: Allow for selection of a specific standard, based on unique needs, and Verify the overwriting method has been successful and removed data across the entire device. Permanent data erasure goes beyond basic file deletion commands, which only remove direct pointers to the data disk sectors and make the data recovery possible with common software tools. Unlike degaussing and physical destruction, which render the storage media unusable, data erasure removes all information while leaving the disk operable. New flash memory-based media implementations, such as solid-state drives or USB flash drives, can cause data erasure techniques to fail allowing remnant data to be recoverable.Software-based overwriting uses a software application to write a stream of zeros, ones or meaningless pseudorandom data onto all sectors of a hard disk drive. There are key differentiators between data erasure and other overwriting methods, which can leave data intact and raise the risk of data breach, identity theft or failure to achieve regulatory compliance. Many data eradication programs also provide multiple overwrites so that they support recognized government and industry