File System Scanning:
When files are deleted, the file system (e.g., NTFS, FAT32, HFS+) marks the space occupied by the file as free, but doesn't immediately overwrite the data. Recovery software scans the file system for "orphaned" data blocks that no longer have references but haven't been overwritten yet.
Signature-Based Search:
Many tools use signature-based recovery, where they search for known patterns or "signatures" of files (e.g., file headers, footers, or specific data structures). This allows the software to recognize files even if their file names or metadata are lost.
Raw Recovery:
For severely corrupted or unrecoverable file systems, raw recovery can still find individual pieces of data based on known file formats, despite missing file system references. This is often used when files are lost due to system crashes or damaged file structures.
Preview and Restore:
Most software allows users to preview recoverable files (e.g., images, documents) before restoration. Once files are located, the software copies them back to a safe location, such as another drive, to avoid overwriting.
Storage Device Considerations:
Data recovery tools can be used on HDDs, SSDs, USB drives, SD cards, etc., but the chances of success depend on the state of the device and whether the space previously occupied by the deleted file has been overwritten.