I ran a "full format operation" (unchecked "quick format") on my disk. Does this remove data in a secure way? I have read answers for related questions and looked on Wikipedia, but am still unclear how it works.

I feel like it doesn't fill every byte with zeroes, but instead it just checks for bad disk sectors and reallocates them. I'm mainly looking at security aspects for this question. It looks my disk is insecure for data restore.


Info for Windows Vista (and I presume 7) Apparently a "full format" in later Windows versions does indeed overwrite each sector.

  • I accept this one since this post was tagged as "win7". But AndrejaKo answer is correct for pre Vista windows! Also we need real proof that it actually works at Win7. – ShyMan Oct 30 '11 at 20:00
  • "Proof" can be had by examining the (unmounted) disk with any hex/disk editor, such as HxD on Windows. All the unallocated sectors will contain nothing but zeros. There is really no way to determine if a sector is bad or not without actually writing to it and reading back the result. – kreemoweet Oct 28 '19 at 19:27

A quick format just deletes the allocation table and leaves the files in place.

On the other hand the full format DOES NOT go through the whole partition and erase data ON PRE-VISTA VERSIONS OF WINDOWS. What it does is basically scandisk and quick format. This way if there are any errors on the disk itself, they will be found and bad blocks will be marked as such and possibly replaced by spare blocks by the HDD. This way we can be sure that the formatted partition is physically in good condition and may be used.

Here's a source form Microsoft that backs that claim.

  • 2
    Thank you for Microsoft source. Let's wait for other answers, I will accept your answer later. – ShyMan Oct 30 '11 at 8:48
  • deleted mine and +1 to you! – William Hilsum Oct 30 '11 at 16:07
  • @Moab Thank you for notifying me of this. I actually spend quite a while looking for procedure in windows 7 and vista on the suppot site but couldn't find it. – AndrejaKo Oct 30 '11 at 20:07
  • @Moab Wouldn't that be stealing kreemoweet's upvotes? – AndrejaKo Oct 30 '11 at 21:27
  • @AndrejaKo These 2 answers complement each other. I would like to accept them both, but site doesn't allow that. – ShyMan Oct 30 '11 at 21:32

Full format post-Vista will supposedly zero the drive, ensuring that all data is erased. If the formatting that is done obeys the Microsoft documentation, the data will be completely erased.

A forensic lab equipped with the right equipment can still "peel back" layers of magnetism to peek at older data, even if it was over-written several times. But this should not concern you, unless you are in trouble with some national security agency.

Your disk manufacturer may supply a "low level disk format utility". Nowadays, low-level formatting no longer applies to modern disks, so these utilities just reinitialize the disk to all-zeroes and try to resurrect bad sectors, but I would trust more such a utility to correctly reset the disk than the Windows format utility.

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