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What algorithm does windows drive formatting utility use to format a drive? is it different from 'Simple Overwrite' (1 pass) ?

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3 Answers

up vote 4 down vote

A Quick Format only rewrites the MFT, which is what makes it fast. A full format forces the OS to do a bad sector check. If you do a full format from Vista or later, then zeroes are written to the entire drive as well.

Source: KB 941961

The format command behavior has changed in Windows Vista. By default in Windows Vista, the format command writes zeros to the whole disk when a full format is performed. In Windows XP and in earlier versions of the Windows operating system, the format command does not write zeros to the whole disk when a full format is performed.

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Did not know they changed the behavior, thanks for the link. – Moab Feb 14 '11 at 16:36
Long format doesn't check anything : It just rewrites. This has the side-benefit of refreshing the magnetic disk and "fixing" bad sectors. – harrymc Feb 14 '11 at 17:08
@harrymc: No, actually there's no rewriting of anything going on in XP. – afrazier Feb 14 '11 at 19:06
I do remember having "fixed" hard disk errors in XP via full format, which was also MUCH longer than quick format. According to you, both full and quick formats should have roughly the same speed. – harrymc Feb 14 '11 at 19:17
@harrymc: No, a full format still does a bad sector check in XP. That still takes a long time, as chkdsk /r can verify. – afrazier Feb 14 '11 at 21:42
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up vote 2 down vote

XP and before Windows Long format does not overwrite the drive, it rewrites the MBR and MFT, then does a surface scan for bad sectors on the entire disk, which is read only.

http://support.microsoft.com/kb/302686

Data recovery is still possible after a XP Windows long format because only the MBR and MFT are overwritten.

You would need to use a 3rd party utility to overwrite the entire drive before data recovery becomes impossible.

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up vote 1 down vote

There is a difference between fast format, that just re-initializes the disk tables to empty, and long format that rewrites all the sectors in one pass.

This is probably exactly the same as what you call 'Simple Overwrite'.

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what are disk tables? Does overwriting disk tables makes you lose all data? – user2233 Feb 14 '11 at 15:51
Data is logically lost in fast format, but not physically. A professional will still be able to retrieve the files (this is what most file-retrieval programs do). Slow format erases the data, so only the CIA etc. can still retrieve it, and disk-nuking products with multiple passes make even this unlikely. – harrymc Feb 14 '11 at 16:17
Of course, this assumes a classic "spinning magnetic platters" hard disk. The question appears to ask about "drives" in general, and it's important to note that it's impossible to erase flash drives using sector writes, because of the sector remapping done by wear leveling algorithms. Only the drive's own "secure erase" command can write to every single block. And even spinning disks can have similar remapping in place to deal with bad blocks. – Ben Voigt Feb 14 '11 at 16:50
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