Accidentally Formatted my data drive. Can it be undone?

Started May 14, 2012 | Discussions thread
newmikey Veteran Member • Posts: 4,735
Re: Best option to unformat:

Sean Nelson wrote:

Are you using Windows? There's a "Quick Format" checkbox on the Format dialogue box you get by either:

  • Right-clicking the drive in Explorer and selecting "Format", or
  • Right-clicking the partition in Disk Management and selecting "Format"

If you're using Windows tools then you need to know that a format actually will erase all the data on the drive if you don't have that "Quick Format" option checked.

I do not use Windows anymore (and haven't for quite some time now) so my memory only serves me as far back as XP. Any format action ever designed under DOS or Windows only ever did 3 things, as described on Wikipedia:

Format is a command-line utility included in Microsoft DOS, IBM OS/2 and Microsoft Windows operating systems to produce disk formatting.

The command will perform the following actions by default on a floppy drive, hard drive, solid-states (USB), or other magnetic medium. It will not perform this function on optical media.

  1. The FAT entries are cleared by changing them to 0x00.
  2. The root directory is cleared out by changing any values found to 0x00.
  3. Format then checks each cluster to see if it is good or bad and marks it in the FAT.

Optionally, (by adding /s, for "system") it can also install a volume boot record. When this option is included, bootstrap code is written to the first sector of the volume (and possibly elsewhere as well). FORMAT always writes a BIOS Parameter Block to the first sector, with or without the /S option.

The "format" command does not zero any sectors. Contrary to what you are trying to convince me of(I think if I understood your post correctly) therefore even a full format is not in- and by- itself destructive to the data on the drive. Testdisk wil:

1. reconstruct the FAT entries

2. reconstruct the root directory

With that, to all intents and purposes you should have the disk back in perfect order unless the disk had so many bad sectors that some entries couldn't be put together again.

According to Microsoft itself, the only difference between quick format and full format is the cluster check itself:

When you choose to run a regular format on a volume, files are removed from the volume that you are formatting and the hard disk is scanned for bad sectors. The scan for bad sectors is responsible for the majority of the time that it takes to format a volume.
If you choose the Quick format option, format removes files from the partition, but does not scan the disk for bad sectors. Only use this option if your hard disk has been previously formatted and you are sure that your hard disk is not damaged.

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