The Reason Why When You Delete Files, They Aren’t Erased

I work in the tech industry, and one question people often ask is whether or not I can retrieve a file that was accidentally deleted. On the other hand, you might want to know how to permanently delete files from your computer to prevent someone from retrieving them. Before I get into the details to answer these questions, I’d like to explain the three types of drives people usually have in their computers.

SSD (solid-state) drives are the newest, fastest and most expensive drives. They typically offer a lower storage capacity due to their high cost. HDD (traditional hard disk) drives use an older technology and are the slowest and most affordable drives. They typically have the largest storage capacity. Hybrid drives offer a compromise by combining SSD and HDD technologies, thus creating affordable faster and larger capacity drives for only slightly more money than traditional HDD drives.

Let’s say you delete files or photos that you then want to retrieve. If you have a traditional hard drive, and if you stop using the drive soon after you’ve deleted the file, chances are, it can be recovered.

If you delete files using a SSD drive, things can get a little tricky. SSDs utilize NAND memory chips which are used in the fastest, current computer models. Unlike RAM memory that is erased when you turn off your computer, data stored on the NAND memory chips is retained after the computer is turned off and can therefore be used the same way a traditional hard disk drive is used.

SSDs store data on the NAND chips using an embedded processor called a controller. The controller encodes and decodes the data in a way that the computer can understand. Different controllers use different methods for encoding and decoding data to the NAND memory.

Recovering data from a SSD requires a detailed understanding of how a specific controller writes data to the NAND memory on the SSD. Because there are many different SSD manufactures with different types of controllers, the recovery process quickly becomes very complex.

A traditional hard drive (HDD) has spinning platters full of data. When you delete files on this type of drive, you don’t really delete the file. Instead, you delete the pointer that points to the location of the file on the hard drive. The data itself will remain on your hard drive until it’s written over. The next time you download a file or install software on your drive, the data on the platters can be overwritten.

So, if you accidentally deleted a file a long time ago, chances are, it’s already been written over. However, if you deleted a file this morning, it can probably be retrieved, if that makes sense. The best way to think of this is that deleting files is not the same as erasing the information.

Like SSD drives, Hybrids require more complex recovery methods to recover data. In other words, there are too many variables to make sweeping generalizations about how retrieving deleted files works on Hybrid drives. However, it’s safe to say that with the right hardware, software and enough tech savvy, it’s possible (not always probable, but possible).

All of the examples I have given so far assume that there is no physical damage to your drive. Drives that have physically failed will often make a clicking or grinding noise. Some failed drives make no noise at all and do not show up when you connect them to your computer.

If you delete files on a drive that then fails, it’s more complicated. These drives require physical repairs before software tools can be used to recover data from them. This repair process dramatically increases the cost of recovery.

If you delete files or photos that you want to make sure nobody ever finds, the best thing to do is take your hard drive out of your computer and replace it with another one. I don’t even trust reformatting a drive (some people say it’s possible to recover data from a reformatted drive, although that would only be possible in remote circumstances). In my opinion, completely replacing the drive is the only way to be 100% sure your data will not be found.

It’s important to keep these things in mind if you are recycling your computer. There have been countless stories of people who think they have permanently deleted everything from their computer, then they give that computer away, and then someone recovers their personal information.

If you would like to know how to permanently delete files and photos from your computer, I suggest you click over to How to Permanently Delete Files from Your Computer [Infographic].

Photo Credit: Bill Dickinson

  • Preeti N

    Thank you Diana please write more about computer science and infosec! So nice!

    • dianaadams

      Hi Preeti,

      Wow, that is really nice of you. Thank you very much! 🙂 And, I will. 🙂


  • New is always better

    Is there new data storage technology on the way?