How can AVG Undelete recover find deleted files on my flash drive?

imagine a hard drive like a text book. there is an index at the front that tells you where to find sections. a file has an entry in the index. when you delete a file, you just erase the index entry and mark the space as empty to be reused whenever the space is needed. that way, the next time you go to write a file, you look in the index for empty space and find the area where the old file was deleted. you go to the section of the book and start writing in the same section safely knowing that even if there were contents there, they were not in use.

AVG Undelete and other forensic analysis tools look through the contents of the drive itself (reading the book rather than just the index) to find files.

this is done not just on flash drives, SSDs, but also regular hard drives and even optical drives.

this is because you don't want to waste time physically erasing a space when it doesn't need to be.

there are some forensic analysis tools that are so good at doing this sort of retrieval that they can in some cases recover sections of files that were overwritten (files don't always write sequentially, often time, they have holes or their data is spaced out - this is called fragmentation). if you truly want to make sure that data is erased, the best thing to do is to physically destroy the hard drive like drilling a hole through the disks or taking a hammer and hitting it many times very hard.

when you delete a file, it doesnt actually delete it, what happens is it gets moved to a "reusable" section of the drive that can be overwritten with data.

This makes it possible to retrieve data that has not been over written.