Question Can I install Windows 8 from USB to an External HDD, on Windows 10?

[lgdl_y]

I have a desktop running Windows 10. I own an empty HDD, and a USB preloaded with Windows 8 (and I have activation key).

I would like to install Windows 8 on the external HDD so that when it is plugged in, I can choose to either boot from Windows 8 or Windows 10.

Do I need to format my external HDD? Does it have to be FAT32 or NTFS? I would like to not mess with the existing Windows 10 OS which is present on C:

Any resources would be greatly appreciated, it is my first time doing this.
Thanks

 

[Eximo]

I don't believe Windows 8 will run on FAT32, but don't quote me on that. Any disk larger than 37GB should be running NTFS or something else with journaling in my opinion. Can't say I have ever tried any of the NT OS without NTFS, just doesn't seem to make any sense to do so.

This gets a bit tricky. If you want Windows 10 and Windows 8 in the same boot loader that means relying on the Windows 10 drive. In other words, you wouldn't be able to boot the OS from the external drive without the other drive in place.

Were I you I would simply unplug your Windows 10 drive. Install Windows 8 on your external drive and use the BIOS to select your boot device. Usually a shortcut key you can use when you start the computer to get into a quick select boot menu. That way you have two independent OS. Once you plug in the Windows 10 drive they would be able to see each others disks.

You might at this point be able to still edit your boot loader. https://docs.microsoft.com/en-us/windows-hardware/drivers/devtest/adding-boot-entries

You can also just open the file in a text editor and add another boot line option. Either way, this is how you get a menu for having multiple OS.

 

[Alabalcho]

Unplug your existing Windows 10 drive from the system, and boot only with Windows 8 media, and that external drive. If setup will let you install there, go for it.