For some reason the Windows 8 x64 Pro ISO that I got from TechNet and the Upgrade ISO is different. Is there any reason for the differences? One of the big ones is size. The downloaded ISO from the upgrade program is ~0.6GB smaller than the one I pulled from my TechNet account. TechNet ISO: A5889F86 Upgrade ISO: 6F8E5826 P.S. - Found the difference in size in the install.wim file. Why is it smaller?
The upgrade ISO uses a compressed/encrypted .esd file instead of a .wim file to pack the base installation.
also the Upgrade Assistant checks for time and date before it builds the ISO and writes that information to ISO file, so even two upgrade ISOs will be different in hash... also some ISO from Upgrade Assistant have already included available Windows Updates...