My Google search for ""does installing windows format the hard disk" returns: No results found for "does installing windows format the hard disk". I was quite surprised.

I'm hoping to get a quick answer here. Does an install format the hard disk, and destroy all data, including non-os/s data? -Or do you specifically have to say "format" at some point so you know you are losing everything? [I tried to go to SP3, but it doesn't work on my computer. My SP2 disk is fired. I only have a SP1 disk, with a seperate SP2 package. I can't get to Safe Mode to uninstall SP3 ("Windows XP Setup cann run under Safemode. Setup will restart now.). I don't want running the SP1 disk to destroy any non-o/s data.]


  • 1
    it can, tho it doesn't have to. you should seriously consider backing up your data to another drive/partition, then create a smaller system partition to format & install windows to. any other space can be formatted & used as a data partition, and if this happens again you can just format & reinstall without worrying about overwriting your data. Apr 20, 2010 at 23:36

1 Answer 1


There is a specific procedure to perform a repair installation to get Windows working again, and your data should be preserved. However, you should backup your data first, just in case something goes wrong.

Be sure to follow the instructions exactly, or else the Windows installation may format your drive.

  • I can't get to the point to select repair. It wants to continue the previous install, which fails with the following error "the signature for windows xp professional upgrade is invalid" error code 800b0100 - after having ran for a couple minutes.
    – Carl
    Apr 21, 2010 at 0:13
  • I got it to the point where repair would be an option, but there's too much damage. I'll have to reformat.
    – Carl
    Apr 21, 2010 at 3:52
  • Bummer, sorry to hear that. If you haven't already backed up the data, at least you can use a different computer to burn an Ubuntu Linux Live CD. Then you can boot your PC, attach a USB drive, and copy your files. You might also be able to reinstall Windows without formatting. If you reinstall, you can either install over the existing C:\WINDOWS directory (wiping out its current contents), or install to a different directory, such as C:\WINXP.
    – rob
    Apr 21, 2010 at 19:30

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