I just upgraded from Windows 7 to 10, thinking it would make a clean install I backed up everything. Now that it's installed, old files are still there in C:/, there is hardly any disk space left.

  1. How do I clean all the files from the previous install? Will it clean up all the disk space? Most of them are in windows.old folder I suppose.

  2. Clean install again. How?

  • Use the Cleanup Tool. If you want a clean installation run the installer again and you will be provided an option to lose your application and personal files. If you want them just use the tool to delete Windows.old
    – Ramhound
    Nov 8, 2014 at 13:27

1 Answer 1


There are two kinds of installs:

  1. Clean installs (aka format and install, or wipe and load)
  2. Upgrades.

You selected upgrade so it did not do a clean install. Instead it tried to keep as much old stuff working as possible.

As to how to do a clean install. Just use the install medium again. In the first part of the disk format the old partition. That will yield a clean guaranteed install. There are tools to reclaim space and doing that and defragmenting might yield the same disk space. Might. I clean install is fast en sure and it is the method I always used.

Note 1: Windows 10 is a preview. Do not try to use it as a main OS. Support for it will end and there is typically no way to upgrade previews to the full version. So if you want to move to windows 10 in a couple of months you will have to do another install.

Note 2: It is a previous, with possible bugs (heck. Likely bugs!) and with extra logging. Do not use it for anything else than testing. E.g. do not use it for Internet banking, on-line purchases or anything privacy related.

[Edit: Tested windows cleanup - system files]

Starting with a clean installation of windows 7 to test with.

Disk space used after a clean windows 7 installation

Starting the windows 10 preview iso and selecting upgrade (thus keeping old files)

Install win10 preview

Installing on the same disk/partition as the previously installed OS.

over the old OS

Now running windows 10. Not much disk space left with the old folders still present.

disk space after upgrading win7 to win 10 preview.

finally! Running the cleanup.

search "disk cleanup" - system files -


results after the cleanup

  • OK, so this leaves two option, 1. Wait for stable windows 10 and clean install it. 2. Clean Install Windows 7. By the way, when I was installing, I chose Keep NO files, and it just removed the stuff in Downloads/ etc while all the stuff in Program Files is still there. Nov 8, 2014 at 14:13
  • In Disk Space I have, 70.4 GB available of 218 GB. While the windows.old folder is only 40GB. Where did the rest of the space go then? Nov 9, 2014 at 7:03
  • Hennes, yes there are and they are all mounted. imgur.com/RNZHIkW Nov 9, 2014 at 11:10
  • In that case I am almost out of idea. Last two : 1) if to boot a liveOS (from CD or pendrive) and to a disk usage on the HDD (e.g. a du -sch /mnt/ from a unix liveCD or something via Hirens). 2) How big is the disk in the BIOS? (Really far out since something needs to have changed the host protected area).
    – Hennes
    Nov 9, 2014 at 11:20

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