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What does “Delete” really do?

Posted by Serges LaRiviere on Sat, Feb 25, 2012

Dear Techie,

I work from home and as a result end up with a lot of things on my hard drive that I want to securely delete.  I know that when I “delete” something it goes to my Recycle Bin.  How do I make sure that when I get rid of something it cannot be brought back?


D. Liet


Hi D,

When dealing with windows, there are three “levels” of deletion.

First Level: Recycle Bin

When you first delete a file in Microsoft Windows it by default goes into your Recycle Bin.

The Recycle Bin temporarily stores your files until you decide to really delete them, or restore them.  It’s a safety-net in the event you ever want your file back.

By default, Windows will automatically ‘empty’ the Recycle Bin when the contents reach 10% of the total available storage space on your hard drive. For most systems this means there can be a lot of old files in the Recycle Bin at any time!

Second Level: Deleted from disk

If you decide to empty your recycle bin or delete a file by bypassing the recycle bin (using Shift-Delete), your file is considered to be officially deleted.  This removes the location of the file from the “File Allocation Table” or FAT which is a record of the physical location of every file on your hard drive.  For those of us born before 1990, if you think about your hard drive like an old record, the FAT is like the track list on the record sleeve.  Without the track list, you would not know that track 4 on side B was where the song Breathe was located on your LP of Dark Side of the Moon.  By removing that entry in the FAT, you allow the hard drive to eventually write back over that section of the disc.  Unfortunately, since all you’ve done is essentially make the computer forget where it put that file, it is still possible to “un-delete” the file and return it’s entry to the FAT.

Third Level: Secure Delete

To have a file be really, truly removed from the hard drive, it first needs to have the FAT entry removed through the “deleted from disk” step.  After that step is complete, the area of the hard drive where the file is written must be overwritten.  This can happen naturally as over time you will likely use that same space over and over, but if you have a file that absolutely, positively must be removed, you need to use a program that can securely delete a file.  Many proper internet security programs have a secure delete function built in, although if your does not you can find them online for free (I’ve used and tested “Zilla Data Nuker” and “CCleaner” which both work great).  I do caution any user that tries any secure delete program as anything that is securely delete CANNOT be recovered.  Read the instructions carefully; some programs have the ability to completely wipe your hard drive of all data.

Secure deletion is also important if you plan to give away or sell a computer.  Making sure that your financial and personal data is safely deleted from a computer when you dispose of it is very important and is a good practice for home users and businesses alike.  If you need help your local computer repair shop can help you make sure that what you want gone is truly gone.

Hope this helps!

The Techie


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