What deleting actually does
A storage device keeps an index of where each file lives. Deleting a file removes its entry from that index and marks the space as available.
The contents stay exactly where they were until something else happens to be written on top. That may be minutes later. It may be never.
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Deleting a file
Removes its entry from the index. The contents stay where they were.
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A quick format
Rewrites the index and nothing else.
Why formatting is barely better
A quick format rewrites the index and nothing else. The files are still there in full; the drive has simply forgotten where it put them. This is why consumer recovery software can pull back photos from a drive that appears completely empty.
What actually removes data
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Secure erase
The drive's own controller purges its contents, including areas the operating system cannot reach. The right tool for a drive that will be reused.
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Full overwrite
Works properly on mechanical hard drives; unreliable on SSDs because of wear levelling and spare capacity.
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Physical destruction
Final, and appropriate when a drive is being retired rather than resold.
What this means if you are selling
If you hand over a drive you deleted files from, you are handing over the files. That is not a reason to panic — it is a reason to make sure whoever takes it actually erases it properly.
Every storage device we buy is securely erased at no charge after the purchase, watchable on request, with a Certificate of Data Destruction if you ask for one. The whole process is here.
Common questions
Is my data at risk if I sell a PC without wiping it?
It depends entirely on who you sell it to. Handed to a stranger from a marketplace listing, yes — the files are readable with free software. That is one of the few genuinely good reasons to sell to an established business rather than a stranger.
Should I remove the drive instead?
You can. Keep the drive and sell the rest of the machine — it is a normal request, and the offer is just lower without it.