replacing win 10 with win7

[rtrg1]

please bear with me, again a short story is needed. I am buying the above desktop or an 8100,8200, or 8300 for a friend. ALL have win 10 64 bit installed by the sellers or a wiped HDD. I do not know if win 7 32bit or 64bit were preinstalled. in my case win7 32bit WAS preinstalled. I burned an ISO and cloned several HDDs for spares. I used an unused COA non HP COA product key that matched my edition to activate the ISO. worked perfectly. the HP COAs attached to the cases did NOT work. the cloned HDDs are activated from the installed ISO OS including all my apps.

what I have in mind is to simply replace the win 10 hdd or wiped hdd with one of my clones. will this work? it has worked for me in the past. my friend is used to win7 and does not like 10. in addition we will have similar desktops with the same apps in case she needs my help. she is not tech savvy so this is my project. I was told that the HP COA is NOT a real product key for activation. my non HP coa as I said DID activate. in addition a key finder app found the SAME key for both desktops different from the attached COAs. is this common?

if I install both OSs is there a screen displayed that asks which OS is to be used? can win7 be the default? so that this choice does not have to be made every time? does the storage size of the HDD matter, as in replacing a 160, or 250 with a 500? would I be better off using the ISO and then install the needed apps?

[TheOldMan]

The elite 8000 CMT  PC's may have come with Windows 7 installed from the factory.  If that was the case, then Windows 7 can be reinstalled using the HP OEM key that was/is present by a BIOS arrangement.  That PC can use more than 4GB of memory, so if it came with 8GB or more then it probably was 64bit Windows.  

Windows 7 uses a different type of key than newer versions of Windows.  Using the BIOS arrangement is different from the COA on the case.  If the COA on the case was used before or is for a different version of Windows, then it will not work.  If the version Windows 7 you installed was aware of the BIOS arrangement, it would have applied the HP OEM key and activated once it saw the internet.  Many HP Business class PC's came with Windows 7 Pro, so it might be possible to install a Pro OEM OS, using the same method but a different key.  Just an FYI.

If you would PM the key the key finder displayed, I can tell you which method you are using to activate the Windows you have installed, but from the description, it sounds like the OEM key is being used, since more than one PC is using the key.