The data is most often salvaged from storage media such as internal or external hard disk drives, solid-state drives, USB flash drives, magnetic tapes, DVDs subsystems, and other electronic devices. In the meantime, the original file contents remain, often in a number of disconnected fragments, and may be recoverable if not overwritten by other data files.
Such cases can often be mitigated by disk partitioning and consistently storing valuable data files on a different partition from the replaceable OS system files. In a third scenario, files have been accidentally "deleted" from a storage medium by the users. Sometimes data present in the computer gets encrypted or hidden due to reasons like virus attack which can only be recovered by some computer forensic experts. If a drive recovery is necessary, the drive itself has typically failed permanently, and the focus is rather on a one-time recovery, salvaging whatever data can be read. The term "data recovery" is also used in the context of forensic applications or espionage, where data which have been encrypted or hidden, rather than damaged, are recovered.
This can be easily accomplished using a Live DVD by booting directly from a ROM instead of the corrupted drive in question. The techniques employed by many professional data recovery companies can typically salvage most, if not all, of the data that had been lost when the failure occurred. A common misconception is that a damaged printed circuit board may be simply replaced during recovery procedures by an identical PCB from a healthy drive. This type of data recovery can be performed by people without expertise in drive hardware as it requires no special physical equipment or access to platters. Data carving is the recovery of parts of damaged files using knowledge of their structure. Sometimes data can be recovered using relatively simple methods and tools; more serious cases can require expert intervention, particularly if parts of files are irrecoverable. In some cases, data on a hard disk drive can be unreadable due to damage to the partition table or file system, or to (intermittent) media errors.