I recently upgraded two brand new off the shelf "computers" to Windows 10 and a couple of precautions saved me a whole lot of time. I say "computers" in quotes because one was a cheap 10" tablet from WalMart and the other is a cheap stick computer I am now using as a media player. Both computers are the 2GB RAM, 32 GB eMMC type computers with Intel Atom processors and Windows 8.1 + Bing. I also have 9 other computers in my house already on Windows 10 so I was not worried about making a recovery drive because I knew I had the other computers to make one.
1. First thing, create a local user account and install Macrium Reflect Free. There is an option during the setup program to download just Reflect or to also include Windows PE. All you need at this point is just the Reflect program by itself which is about 40 MB. First thing we are going to do is make a backup image, so the less we have installed the smaller the backup image will be.
2. Both these computers had microSD slots so each one got a 32 GB microSD card inserted. Ran a full image backup to the microSD card. Of course you would use a USB flash drive or USB hard drive without microSD capability. Explore the image in Macrium Reflect after it is done and make sure it has all the partitions included in it.
3. My microSD cards both got drive letter E:\. I created a folder on each card called E:\DriversW8. From an elevated ("run as administrator") command prompt I ran:
dism /online /export-driver /destination:E:\DriversW8
This exports all the drivers installed that are not native to Windows to the created folder.
4. I wanted the stick computer to have Windows Pro on it because I want to be able to remote desktop into it. I changed the Windows 8.1 product key to a Windows 8 Pro product key and did the upgrade. I checked to make sure it was activated, and it did activate online. Then I ran gatherosstate.exe from Windows 10 installation USB flash drive and captured the genuineticket.xml file. If you do not have a Windows 8 or 10 product key in bios, or you want to upgrade a version of Windows that you had to manually enter a product key for, you need to do this. It won't hurt to do it even if you do have a product key in bios, it only takes a couple minutes.
4. Using Windows 10 build 10586 installation USB, I selected custom install. I deleted all the partitions in the eMMC ("hard drive"). Installed Windows 10 to the unallocated space. Windows setup automatically read the product key in bios and installed Windows 10 Home. They both activated online because of the product key in bios.
5. Look in device manager and there were quite a few "unknown devices" and one device with an exclamation point. Right click on each one and first select the automatic method for updating device drivers. About half the unknown devices pulled drivers off the internet. For the devices that did not pull drivers online, I selected the option to search computer (or something like that) and browsed to my E:\DriversW8 folder. Each device pulled a driver from there. Also check your display adapter and make sure it isn't Microsoft Basic driver.
6. During step 5 Windows update also kicked in, updating some drivers and installing the cumulative update.
7a. The tablet had a couple issues. No screen rotation. Had to manually install a legacy driver for that by right clicking the very top entry in device manager and selecting install legacy hardware. Had to point it to the specific .inf file in my E:\DriversW8 folder (thank you Google!). Now the screen rotated but it was either upside down or 90 degrees off. More Google searching revealed there is a registry entry required to correct the orientation. Now I know there is a way to load the registry hive from the backup image, but I didn't want to take the time to figure that out. So, installed Macrium Reflect full install this time, Windows PE and all. Ran the option to make a boot entry for Reflect (which runs from Windows PE). Saved a backup image again of the entire eMMC memory. Rebooted into Macrium Reflect from the boot menu. Restored the previously saved Windows 8.1. Found the registry entry and exported it. Rebooted into Macrium from a rescue flash drive I had with Windows PE again, restored the Windows 10 image. Imported the registry key. Screen orientation all good now!
b. Second issue was that Windows 10 replaced the imaging device driver for the two cameras with the wrong driver. Had to go to device manager and update device driver and manually pick the specific .inf file from my E:\Drivers8 folder. That made the cameras work.
8. Now for the upgrade to Pro on the stick computer. Changed the Windows 10 product key to the generic Windows 10 Pro product key everyone gets from an upgrade. It upgraded to Pro but did not activate (expected). Changed the product key again to my Windows 8 Pro product key. Got an error back that the key was in use on another computer (not expected)?!? Ummm...HELLO! It was previously used on this same computer! So I copied the genuineticket.xml file I had saved from Windows 8 to the proper folder in Windows 10. Rebooted. Activated immediately.
Three important steps saved a lot of time/headache. Make a backup image of the current OS. Export the drivers from the current OS. Capture the genuineticket.xml file from the current OS. Then upgrade!
Hope this helps someone.