This apd army mil pdf files r25 always free of charge. Sync your files with the cloud! Various techniques have been developed to counter data remanence.
Effective application of countermeasures can be complicated by several factors, including media that are inaccessible, media that cannot effectively be erased, advanced storage systems that maintain histories of data throughout the data’s life cycle, and persistence of data in memory that is typically considered volatile. UNMAP command to let the drive know to no longer maintain the deleted data. Finally, even when the storage media is overwritten, physical properties of the media may permit recovery of the previous contents. The data may still be recoverable, but not without special laboratory techniques. Clearing is typically an administrative protection against accidental disclosure within an organization. Purging, proportional to the sensitivity of the data, is generally done before releasing media beyond control, such as before discarding old media, or moving media to a computer with different security requirements. The storage media is made unusable for conventional equipment.
Effectiveness of destroying the media varies by medium and method. Conversely, destruction using appropriate techniques is the most secure method of preventing retrieval. A common method used to counter data remanence is to overwrite the storage media with new data. Overwriting is generally an acceptable method of clearing, as long as the media is writable and not damaged.
The simplest overwrite technique writes the same data everywhere—often just a pattern of all zeros. At a minimum, this will prevent the data from being retrieved simply by reading from the media again using standard system functions. In an attempt to counter more advanced data recovery techniques, specific overwrite patterns and multiple passes have often been prescribed. Software overwrite may also be problematic in high-security environments which require stronger controls on data commingling than can be provided by the software in use. There are specialized machines and software that are capable of doing overwriting. The software can sometimes be a standalone operating system specifically designed for data destruction.