Possible to use the same ssd for a Windows and a Mac laptop via different partitions? So my main laptop is a MacBook which runs on a Samsung 850 evo ssd, has 2 partitions- one runs El Capitan and other is formatted as exfat.

My questions is - how can I use this very ssd to run Windows 10 on my other (HP) laptop off the exfat partition?

Situation as of now - I have a bootable usb of Windows 10 but it asks for a cd disk, and I can't seem to find a way to use the usb.

What I fear is that by using a recovery cd to install Windows, the program might overwrite over all my existing data. What I want is to just install Windows on the exfat partition

I understand that unlike Mac, Windows has to be installed separately for each and every computer, I can't use some other laptops ssd to boot this laptop.

Any help or comments are appreciated. Thank you!

Edit: Im gonna use the ssd as an internal ssd on the HP laptop,  not as an external with an enclosure. Its my fathers old work laptop and i have standing instructions to not to edit anything on it (but the damn thing is  running windows 7), since there will come a day when he'll have to return it. This is why i wanna 'preserve' the partition with el capitan. I will not be connecting-disconnecting it again and again. Jist twice. I have since formatted the partition in NTFS.

**so my ultimate question is this : I have a drive with two partitions,  I want to install windows 10 on just one while the other partition remains untouched. Since its too messy to install windows on 1 device and then port it to other,  I have inserted the ssd in the new laptop.  How do I move forward with the installation? **
I think this might be a better fit for Super User as it's mainly about PC/Windows rather than Mac. 

However, as a rough guide -
you'd do far better to clone the Mac's boot &amp; recovery partitions to a spare drive using something like Carbon Copy Cloner then let the Windows installer [from a PC] just break the whole darn thing - which it will, it will insist on NTFS &amp; will probably set up its own EFI &amp; recovery partitions; and Windows won't boot easily if it's not at the beginning - then use the Mac to restore the 2 Mac partitions afterwards to the end of the disk.  This will likely need 3rd Party software, such as Paragon Hard Disk Manager   

Windows also is not truly portable like macOS, so each time you move it to a different machine it will either crash/fail or require re-authorisation from Microsoft. Windows is also not too keen on booting from a removable drive.

Ultimately, I think buying a second SSD would be simplest &amp; safest.