First, before we can understand how data recovery software works it is useful to understand how data storage works in a computer hard drive or USB drive and how deleting files works. This will be simplified to make it easier to understand but most systems follow something very similar to the description below.
Every file stored is written as a series of blocks of data generally represented by 1’s and 0’s. These files are written out in long bands around a physical hard disk or stored in a series of individual memory cells in an SSD or USB drives solid-state memory. The computer, in order to be fast and efficient, lays out the files on the first empty section it can find that is big enough to hold the file. If the file is bigger than any one open section it may split the file into several sections. It then goes to another section of the disk called a FAT or file allocation table (or the equivalent depending on the filesystem) and that tells the computer where on the disk it stored the file. Each sector of the disk can be written to and rewritten to over and over, you don’t even have to remove the old data to write over it. The FAT keeps everything orderly and keeps the computer from writing over currently used space. (Recoverit is compatible with almost all file systems like NTFS, FAT32, FAT16, exFAT, APFS, encrypted APFS, HFS+, encrypted HFS, HFSX, ext2, ext3, ext4, JFS, RAW, RAID, etc.)
This gives you files spread across a hard disk in thin bands similar to the simplified image above. The blue, green, dark green, and red might all be different files stored on the disk. The white represents empty sections on the disk that can still be written to. When the computer needs to write data to the disk it puts each 1 or 0 of that file into the white sections. To read a file it will move to the track with say the green file and read all that data and then, as guided by the file allocation table, move to the next track the green file is on until it has read the entire file. Hard disks spin at fantastic speeds as low as 1,200 and up to 15,000 or more revolutions per minute. This allows the data to be read or written quickly and yet, as anyone saving a large file can tell you, it can still seem to take forever.
When deleting a file, the computer uses the fact that the disk can be written to over and over again and that you can write over existing data to speed things up. Instead of going and erasing each 1 or 0 of the file it just goes to the FAT and removes the entry for the file. Now when the computer looks for empty space the section the file was in looks like it is empty and it is overwritten. Instead of deleting an entire file you just need to remove a few small blocks. Formatting a disk works the same way. In a format, the entire disk is marked as free space.
The reason data recovery works is due to the file management system outlined above. When you delete a file it may first move to a “recycle bin” in your OS and then when the bin is emptied it marks the space the file once occupied on the disk as empty. But the data in your file is still there until it is written over! For this reason, if you want to recover a file don’t delay, the sooner you get started the better.
Specialized software like Wondershare Recoverit scans through your disk and looks for signs of old files still sitting in those empty spaces. If those files have not yet been written over they can be restored good as new! The folders the files were in might even be able to be restored. Recoverit might even find multiple older versions of the same file and you can compare them before recovering. So if you changed a file many times and need an older saved version it might still exist!
Software like Wondershare Recoverit makes this a very simple process. You can even preview images or video files before you recover them to make sure they are the files you are looking for. If your computer is completely crashed and cannot be booted, the software can create a bootable USB drive and then recover your files from there!