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PhotoRec, Digital Picture and File RecoveryPhotoRec is file data recovery software designed to recover lost files including video, documents and archives from hard disks, CD-ROMs, and lost pictures (thus the Photo Recovery name) from digital camera memory. PhotoRec ignores the file system and goes after the underlying data, so it will still work even if your media's file system has been severely damaged or reformatted.PhotoRec is free - this open source multi-platform application is distributed under GNU General Public License (GPLV v2+). PhotoRec is a companion program to TestDisk, an application for recovering lost partitions on a wide variety of file systems and making non-bootable disks bootable again. You can download them from this link.For more safety, PhotoRec uses read-only access to handle the drive or memory card you are about to recover lost data from. Important: As soon as a picture or file is accidentally deleted, or you discover any missing, do NOT save any more pictures or files to that memory device or hard disk drive; otherwise you may overwrite your lost data. This means that while using PhotoRec, you must not choose to write the recovered files to the same partition they were stored on.PhotoRec runs under most Operating systems and can be compiled on almost every Unix system.Download TestDisk & PhotoRecFile systems:PhotoRec ignores the file system; this way it works even if the file system is severely damaged.It can recover lost files from at leastReiserFS includes some special optimizations centered around tails, a name for files and end portions of files that are smaller than a filesystem block. In order to increase performance, ReiserFS is able to store files inside the b*tree leaf nodes themselves, rather than storing the data somewhere else on the disk and pointing to it. Unfortunately, PhotoRec isn't able to deal with this - that's why it doesn't work well with ReiserFS.Media:PhotoRec works with hard disks, CD-ROMs, memory cards (CompactFlash, Memory Stick, Secure Digital/SD, SmartMedia, Microdrive, MMC, etc.), USB memory drives, DD raw image, EnCase E01 image, etc.PhotoRec has been successfully tested with various portable media players including iPod and the following Digital Cameras:Known file formats:PhotoRec searches for known file headers. If there is no data fragmentation, which is often the case, it can recover the whole file. PhotoRec recognises numerous file formats including ZIP, Office, PDF, HTML, JPEG and various graphics file formats. The whole list of file formats recovered by PhotoRec contains more than 390 file extensions (about 225 file families).How PhotoRec works:FAT, NTFS, ext2/ext3/ext4 file systems store files in data blocks (also called clusters under Windows). The cluster or block size remains at a constant number of sectors after being initialized during the formatting of the file system. In general, most operating systems try to store the data in a contiguous way so as to minimize data fragmentation. The seek time of mechanical drives is significant for writing and reading data to/from a hard disk, so that's why it's important to keep the fragmentation to a minimum level.When a file is deleted, the meta-information about this file (file name, date/time, size, location of the first data block/cluster, etc.) is lost; for example, in an ext3/ext4 file system, the names of deleted files are still present, but the location of the first data block is removed. This means the data is still present on the file system, but only until some or all of it is overwritten by new file data.To recover these lost files, PhotoRec first tries to find the data block (or cluster) size. If the file system is not corrupted, this value can be read from the superblock (ext2/ext3/ext4) or volume boot record (FAT, NTFS). Otherwise, PhotoRec reads the media, sector by sector, searching for the first ten files, from which it calculates the block/cluster size from their locations. Once this block size is known, PhotoRec reads the media block by block (or cluster by cluster). Each block is checked against a signature database which comes with the program and has grown in the type of files it can recover ever since PhotoRec's first version came out.For example, PhotoRec identifies a JPEG file when a block begins with:If PhotoRec has already started to recover a file, it stops its recovery, checks the consistency of the file when possible and starts to save the new file (which it determined from the signature it found).If the data is not fragmented, the recovered file should be either identical to or larger than the original file in size. In some cases, PhotoRec can learn the original file size from the file header, so the recovered file is truncated to the correct size. If, however, the recovered file ends up being smaller than its header specifies, it is discarded. Some files, such as *.MP3 types, are data streams. In this case, PhotoRec parses the recovered data, then stops the recovery when the stream ends.When a file is recovered successfully, PhotoRec checks the previous data blocks to see if a file signature was found but the file wasn't able to be successfully recovered (that is, the file was too small), and it tries again. This way, some fragmented files can be successfully recovered.
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