The Win 10 installer DVD is a matter of interest to me, my desktop pc was an online upgrade from Win 8.1 and my laptop from Win 7 so there are no install disks or serial numbers to work with, does a recovery disk resolve this issue.

Apparently the "free" upgrade is linked to the mac address or some other hard coded id of the motherboard and primary HD.

Swapping out the C drive for any reason scares the hell out of me for this reason