Brilliant, thank you!!

:)

Thank you, genet, for some very useful information. I still have a related question:

You wrote, "I have a Lenovo G580 laptop that came with Windows 8 preinstalled. I have upgraded to Windows 10...

C: occupies most of the hard disk, for the user, D: contain the OS installation files including Lenovo-specific stuff such as control of monitor brightness, speaker volume, mousepad on/off, etc. via...