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 use of a special Fn key. User may re-install by special Lenovo-provided one-button system if cannot boot, etc. There are various Lenovo-specific apps, which are not important to me.
I updated to Windows 8.1, but if I re-install it will re-install 8.0 and I'll have to update again. Now with Windows 10, before I do this (MS has not yet sent me the intitiation process) I need to understand what happens with the D: drive and all the Lenovo-specific functionality that would be installed to the C: drive from the D: drive if I use the one-button restore system.
The UEFI in the BIOS prevents any other OS from being installed, and Lenovo does not allow this to be overridden from BIOS settings for Lenovo G580. I assume the UEFI will allow Windows 10, but have not read it specifically. I want to read it specifically before I install Windows 10 and something strange happen.
After I upgrade to Win 10, will this D: drive remain full of 8.0 installation files? Thus, if I initiate the one-button re-install system, will Windows 8.0 re-install thus forcing me to return to MS and go through the upgrade process to Windows 10 again?