In message ,
Robert in CA writes:
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I think I understand,... were actually going after the
registration key for Windows 10 without actually installing
Win 10. Is that correct? Then at a later date I can install

Not quite. In order to get your machine registered on the Microsoft
servers as being entitled to run W10, you have to actually install W10.
But you can revert to 7 immediately, by any means you like (the simplest
probably being by putting back the drive you cloned before you started
the "upgrade").

Win 10 side by side with Win 7 so I can continue to use Win 7
but can also use Win 10 if I choose. Do I have that right?

More or less.

I do have a spare drive so that's not a problem. I will have to
re-read your instructions on how to do this. True, I have done
repairs before but only with your guidance and help. I need to
take this slowly so I understand what I'm doing and not mess
anything up.

Robert

If you have only _one_ spare drive (and two computers currently running
7), then:

A1. Clone computer 1 (a 780?) onto the spare drive. (If you want to be
doubly sure all is well, swap in the spare and make sure it still boots,
i. e. to make sure you have made a valid clone.)
A2. Do the upgrade to 10. MAKE SURE IT IS ACTIVATED (or whatever the
right term is); see Paul's image for how to do that.
A3. Return computer 1 to W7 - either by restoring from the clone, or
just using it, if it's similar in size to the original.

B1/2/3 - as above, for computer 2 (a 4500?), using whichever drive is
spare at this point.

Provided both computers show their W10 installation is valid,
registered, activated, or whatever the right term is (I can never
remember which is which), you can go back to running 7 on them, then
switch to 10 later (or to dual-boot I think, which is more complicated).
--
J. P. Gilliver. UMRA: 1960/1985 MB++G()AL-IS-Ch++(p)Ar@T+H+Sh0!:`)DNAf

I'm the oldest woman on primetime not baking cakes.
- Anne Robinson, RT 2015/8/15-21