Fix: Cleanup after upgrading from Windows 10 technical preview

I recently replaced the internal hard disk of my old Lenovo S10-3t Tablet PC with an SSD and installed Windows 10 technical preview, but recently realized the hard disk had almost run out of space.

Trying to figure out why, I realized that upgrading from the Windows 10 technical preview version to the final Windows 10 version (this happened automatically via Windows Update), left back a “Windows.old” folder at the hard disk root taking up 3.14GB, as if I had upgraded from Windows 7 or Windows 8 via Microsoft’s free OS upgrade offer (that offer is valid for a year btw, so make sure you don’t miss it).

You’ll notice the Disk Cleanup tool (you can find it by pressing the search icon (magnifying glass) at the Windows taskbar and writing “cleanup”, temporary Windows installation files are also mentioned as taking up an extra 3.22 GB, but there is some double counting there, since I ended up with 5.30GB free after cleanup, from around 200MB I had left on the hard disk before I run Disk Cleanup (note that I already had run CCleaner, but I hadn’t selected the option there to cleanup files from previous Windows installation, since I didn’t expect to have any such).

Note, that Disk Cleanup will even warn you that you won’t be able to restore the machine back to the previous Windows version (aka the technical preview), but why should you care to do so anyway?

Update:

To make some extra disk space and since I use a fast SSD, I had set Windows to compress the hard disk contents (one can set this option by right clicking the disk and selecting Properties), so probably there is no double-counting by Disk Cleanup dialog, it just must be showing the uncompressed space those things it cleans take up. So it could indeed be 3.14GB + 3.22GB of useless space taken up by updating Windows technical preview to the official Windows 10 release via the normal automatic Windows Update process, which is quite a lot.

Microsoft should show some warning to the user about all this extra space taken up (right away after updating and offer to remind them in the future again if they opt to keep the files till they’re confident the latest version works OK) and offer them the choice of cleaning this up

Another interesting thing I notice is that although I had selected the option to compress the drive and it had applied respective attribute to all files (showing a progress dialog), it didn’t remember that setting (not sure if I had set it before the upgrade), so probably it wasn’t compressing newer files.