Eli5: how do computers actually delete information entirely?



How does it physically “forget” whatever coded form it held my word document in for example?

In: Technology

In the case of data on a mechanically hardrive it has to write new information into the specific block that the current info is in, other wise it simply marks that space as containing deleted information so that when it needs a place to write more info, it knows that is available and can overwrite the info there.

The info even if marked for deletion is still recoverable until new info is written in that block

A computer doesn’t truly “forget” data until it gets overwritten by new data.

When you delete or uninstall something, the computer doesn’t really get rid of the data. It just forgets where the data is. So you won’t see it anymore and you can’t tell the computer to find it because it doesn’t even know where to look.

This can be important for data security. When you get rid of a computer, any sensitive information that was never actually written over may still be accessible by a snoop with the tools to read the forgotten data rather than what the operating system thinks is there.

They generally don’t. They just go to the index and delete the reference (called a “pointer”) to that document or file. In rare cases (like government computers) we repeatedly rewrite over the file. That way, you can’t just find the file and add it back into the index of files on the computer.

Rarely, something will go wrong in the hardware (ie a wire will break) of the computer and corrupt a sector, but there’s not much I can say about that.

A regular deleted file is still on the hard drive, the computer just “forgets” where it is. What that means in practical terms is that the directory for that file is deleted, and the computer now sees that space as free, and can write over it when a new file is saved.

To truly delete files, there are programs that write gibberish over the space where the file was, ideally rewriting several times to make sure that the original file has been completely overwritten.

Computers store information like word documents using a bunch 1’s and 0’s, and also use pointers to let the computer know where that file is stored. When you simply delete a file it usually just deletes the pointer file and the computer “forgets” where the files are. To securely erase the files, you would need to rearrange those 1’s and 0’s into other random 1’s and 0’s by using a secure erase program

So, digital storage is not like a book where you write and erase what you wrote, but more like little switches that turn on or off, with the information being in how a group of switches looks like. For instance, let’s say I group every eight switches, and an A is writen as 0100 0001 (with 0 being “off” and 1 being “on”). So, how do you delete it? Well, you can’t, you have to move some switches to write over it, maybe all zeroes, maybe some gibberish.

Computer storage is like a notebook of graph paper. Each page of the notebook has 1,000 squares in it, and you can write a single letter in each square.

You can write many documents into the notebook. To do this, you write a table of contents at the beginning, that says something like “June shopping list, pages 537-539.”

When you decide you no longer need your shopping list, you simply erase the entry for “June shopping list” in the table of contents.

The actual information in the shopping list is still there on pages 537-539, the only thing that’s immediately erased is the entry in the table of contents. But someday when you’re writing new information into the notebook, you might decide to erase and overwrite the new information into the squares on pages 537-539 that used to contain your shopping list. At that point, the shopping list is truly gone.