How do I find the product key for Windows 8.1

Well that solves it I will not be buying then!

It really depends on the configuration of the hardware when you installed the second operating system. If the 1st drive is still connected but designated in the BIOS as a secondary device then Windows setup will still detect is as a system drive. It then modifies the boot code and bootstraps from the 1st disk.

The safest way to do what you describe requires the original O/S drive to be disconnected altogether whilst you run Windows setup on the second drive. Only once setup is complete should attach the original drive..

Then instead of modifying the BIOS each time you want the second  drive to load press the F8 key during the initial start up. This loads the one time boot menu which allows you to select the secondary drive as the boot device.

Quite correct, manufacturers do not supply keys for features. They are bought from Microsoft as a part of the Add Features dialogue.

Product Key from Acer does not work says invalid to add features to 8.1

HairyF i got another one for you if you can oblige me:

I had a question for you regarding Win 8.1 since I can tell you know your stuff re Win 8:

I believe its related to the topic thread in that its regarding the idiosyncrasies of installing Win 8.1Pro and Booting from it:

I have an older ASUS Rampage Extreme III mobo to which i have two Samsung 500GB SSDs SATA connected.  I have run out of space on one SSD and have decided to install Win 8.1Pro (upgraded from my Win 8Pro Product code) on both so that i can start to one of them separately, and see both of them as C drives at different times (why:software will often will only install to a C drive).  When i go to BIOS and change the priority of hard drives, something, i'm assuming Win 8.1Pro, will only load up the LAST SSDs system that i was using and not the other one i am specifying.   I know the difference because of the Volume names of the C drives and what is installed on them: besides one is an 850 EVO 500GB the other at 840 500GB.

 i'll shut down, then startup to the American Megatrends BIOS and specify the other SSD top of the the priority list but it'll still 'leap-frog' that drive and load to the last one i just finished shutting down.  This is baffling to me and it doesn't matter what priority i make the other drive, i can have it last in the list and it'll still boot to that other drive in preference to the other.

The only way i have figured out how to change systems is by physically unplugging the SATA cable from the SSD i don't want to use and only plugging in the other.?? Then i have to plug the other drive back in and add it back in Computer Management tool.  Frustrating time consuming and annoying.

Have you ran across this before or know why this might be happening?  Is there some sort of trail left on shut down Win 8 that it wants to follow or history path on shut down/restart Win8.1Pro uses to identify a hard drive it 'wants' to boot from perhaps if its sees two versions of itself (both upgraded from the same Win 8Pro Prod. Key originally) ?  could that be the problem??

Ideally i'd love to Boot up to one or the other every resart kind of like the Windows screen when it asks if you'd like to start Win normally or in safe mode etc....??

any ideas here?  sorry about the obscure-ness of the probe/question.

thanks