I read some place (probably here) that in time Win10 will remove the Windows.old folder. But now with the boot menu having a "roll back" choice I don't know if it will. My Win10 installation was a clean install from the 1st ISO on a clean partition, and then upgraded to 9879 and now 9926. It was never a Win8 to Win10 upgrade. I have Win10 stored on a 50GB partition of my 256GB SSD. In build 9879 I had about 20GB free but after upgrading to build 9926 I got 13.8GB free (it actually went down as low as 8GB free but then went up again). I got nothing stored except a few MUI apps and Office 365. Documents folder is mapped to the Documents folder on my Win8 partition, Pictures, Music and Video mapped to mSD card. I install desktop programs setting their installation directory to the one for them on the Win8 partition and have even found that many desktop programs installed in my Win8 OS run in Win10 from clicking their shortcut off the Win8 partition without having re-installed them. I will never "roll back" to build 9879. So can I just delete Windows.old?