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How does formatting work in Windows?

Does it erase all the data on the drive to 0? What's the difference between fast format and normal format? If it doesn't set all the data in the drive to 0, how can I do that?

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5 Answers 5

A long format will run a short format and a check disk operation.

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A fast format (sometimes called quick format) only recreates the necessary table structures for the filesystem. The files aren't actually deleted, but when the table structures are reset to it's initial state they will be overwritten in time. This is because the system marked those positions as 'writable'.

A normal format recreates the table structures and clears out every block on the hard drive.

You can manually set the blocks to zero if you want using a tool like 'dd' on Linux.

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I've found that the normal format does not actually clear the blocks either (at least on Windows 9x). It appears to access them all (since it takes so long to run), but at the end of it I was still able to directly read the sectors and pull old data. –  Brian Knoblauch Nov 18 '09 at 12:35

There are 3rd party "Wipe Disk" tools that can really erase the data on the disk.

you can start looking here and google the rest:

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A Quick format will only wipe out the file-system tables (MFT). Files can still be reconstituted.

A Full format will also rewrite all sectors in order to reset all magnetic platters, thereby wiping out all data. Files can no longer be reconstituted, except with special equipment to "peel back" the magnetic layers, which is only in the possession of organizations such as the FBI, CIA etc.

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If it doesn't set all the data in the drive to 0, how can I do that?

neither quick nor full format will erase data on a hard drive beyond recovery, you want to run Darik's Boot And Nuke (aka DBAN) to be sure all data on the hard disk are wiped thoroughly.

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DBAN also wont work for the DCO and HPA sectors of a hard drive. –  Steam Oct 5 '13 at 22:52

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