Formatting before selling your PC

Thank you for the advice. This reminds me that we have 2 extra HDD of 500 GB each that I am planning to sell. When the new computer arrives, I guess it will have a big storage and surely we would buy an external for the archiving so those 3 extra HDD will have no use for us. And those contain mostly photos and videos plus some other important files (obviously only important files are archived). So maybe I should bear in mind to clear the HDD before selling it.

 

Simple formatting is not enough.

There are software can recover files even from formatted hard drives. Actually I have used such software to recover files from accidental formatted hard drives even back in around the year 2000. These days such recovery software are more common.

What you need to do is,
1. Format the hard drive
2. Fill the hard drive again with irrelevant files to full
3. Format it again

That is the minimal requirement to keep your deleted files safe.
Because any kind of deletion (just once) or (just) formatted hard drive can't really hide the files from recovery software. Until you override the same part of the hard drive with some other files, all the files from the previously formatted parts can still be recovered easily.