Think the best analogy I can give you is this:

If you write a check and give it to someone, the money has not yet been taken out of your account until they turn that check into cash or deposit it into their bank account.

Until that time, it is something you are keeping a record of to say “I wrote a check for $700 so I am down $700 in my checking account.” Even though the total balance today says $1700, you know that it really is supposed to be $1000 that is available to be used for other expenses.

If you wanted to recover that $700, all you need to do is shred the check before it gets to the bank or check cashing place or contact your bank to tell them to not process this check. Thereby, you have essentially “recovered” the $700 you intended to give to someone else.

This is similar to how your hard drive works. When you tell your computer to delete a file, your computer’s operating system basically tells you that it’s been deleted and no longer lets you access it by normal methods, but that data still exists in a form awaiting an actual deletion. Once you create a new file, your operating system remembers that it had deleted 100MB earlier in the day, so it can now use 25MB of that 100MB it reserved to overwrite some of that file that was deleted, in a sense. However, this whole time, your operating system told you that you had an extra 100MB immediately after you deleted that file, even though it was really being reserved to eventually be replaced.

Your operating system speaks in binary language of 1’s and 0’s and this file existed as a bunch of 1’s and 0’s. When something else got overwritten, it took some of these 1’s and 0’s from the old file to be turned into space for the new file that is to be created.

So as long as it’s recent, no new data has been written to the drive, and the computer hasn’t been restarted, the file is still effectively there in the binary language, just not in plain text to you. However, as time goes on, new data is written, or the computer is restarted, then it becomes much more difficult to restore the file. This is mainly because data is always being written to the drive due to the computer doing other things in the background in addition to the things you do on the computer.

But there isn’t any way to exploit this as this is all due to how much data is available. You have a 1TB drive in your computer and your computer will only ever report 1TB of available storage. It will never report to you that you have more storage unless you’ve done some trickery and even then, it’s just playing with the numbers that you see. Fake USB drives do this where someone sells you what they tell you is 2TB but is actually 16GB and the file has been written to trick the operating system into thinking it has 2TB. If you try to copy more than the actual 16GB of available space, you get an error.