The process of recovering important data from failed or corrupted storage media is an urgent need that is called data recovery. Many times, secondary storage media like hard drives, flash drives, and compact discs are unable to be accessed through normal means due to corruption or damage. While a computer might not be able to immediately access the data, that does not mean the data is permanently gone.
There are several reasons that data can no longer be accessible. Sometimes it is a software failure, such as an operating system crash that renders the computer unable to boot or be used in a typical manner. In this case, the files will be fairly easily accessible using an external operating system on a networked computer or a bootable live CD to simply transfer the files to a working storage medium. In some software failure cases, there are extenuating circumstances which make it more difficult to obtain the data. This can be either from file system corruption or an error in the disk partitioning. To implement a successful data recovery process in this case requires an advanced knowledge of the file system and, depending upon operating system, the kernel itself.
In other cases, the hardware itself has failed. In this case sometimes physical repair of a hard drive is required. For example, it might have been dropped and the read/write head might have been broken by striking the platter. In others, the printed circuit board itself might have suffered physical damages. This poses unique challenges to hard drives manufactured past 2003, however, because printed circuit board contains a System Area which manages the operation of the drive and is inaccessible to the user and cannot easily be replaced. The hard drive must be opened up and a new read/write head installed. In solid state cases, sometimes the flash memory must be uninstalled and soldered into a new board in order to read the data.
Often, the data is inaccessible not by software or hardware failure but by unintentional deletion. In this case, the data is not actually removed from the hard drive but hidden by the file system. The files are able to be retrieved as long as other data has not been written on top of it. Depending upon how extensively the storage medium was used after deleting the files, retrieval of the files in either full or partially fragmented state is possible.
It is not always necessary for experts to have physical access in order to complete successful data recovery. If internet access is available, often they are able to access the problem remotely and recover the data. In worst case scenarios, involving hardware damage, physical access is required. Special disk-imaging technologies are able to retrieve all readable data from the drive in worst case scenarios where the hard drive has been too damaged to repair. If some data is available but is corrupted or incomplete, in some situations the data can be restructured by a process called data carving. It is recommended to contact a company providing data recovery to assist in the recovery of valuable files.