What is data recovery?

Data recovery software has multiple motivations: the most common range from inadvertent human error, viruses or Police investigation. For example, in the Clearstream affair in France, a portion of the survey was based on data retrieved from the computer of General Rondeau.

The principle of data recovery is as follows: in general, operating systems cut all resources into pieces which they access through index. Thus, very roughly, an operating system, sees a hard drive like an encyclopedia, and the system will use the table of contents of the encyclopedia to quickly access a particular article according to the demands of the users. When the user requests the operating system to erase a structure (a file or a partition, for example), the operating system does not destroy the structure directly concerned. It merely changing the index. Thus, in the metaphor of the encyclopedia, ask the operating system to delete an item, the equivalent of removing the item from the table of contents. The article dropped, even if not included in the table of contents, however, is always there in the middle of the pages of the encyclopedia.

Data Recovery is a difficult task. Indeed, in the presence of backups - whether copies stored in the dustbin of Windows or any tool System Restore, it is beyond the scope of data recovery. In addition, operating systems are primarily designed to use resources effectively to ensure good performance. For example, the user can request the free space to the operating system (to add a new article in the encyclopedia, for example). In this case, the operating system can give pages corresponding to the item deleted the user wants to write a new article. As operating systems are designed primarily to ensure good performance, data recovery is at best an afterthought. It is significant that from version 5, the late MS-DOS provides two tools for data recovery ( "undelete" and "unformat"). Both tools were included in version 6 but were abandoned to the launch of Microsoft Windows 95.