I have a Dell XPS 8930 with two SSDs, 1TB and 500GB. The current Win10 install is on the 1TB in a "C" partition. I also have most of my user data on the 1TB on different partitions (all safely backed up). The 500GB contains only disposable junk data.

As part of a complex diagnostic procedure, I'm going to unplug the 1TB and install a new Win10 on the 500GB. I'm assuming that will clear the 500GB drive and install the OS on a new "C" partition on the 500GB.

When I re-plug-in the 1TB, the system will "see" the original C. Will there a conflict with the new C partition on the 500GB? Or will the system just assign the "old" C to an available drive letter? If there is a conflict, how can I resolve that?

I do not want to change the new OS partition to another drive letter, to ensure that all drivers work, and to avoid any other such problems.

I can move the 1TB to an external USB enclosure and look at it on another computer, possibly re-letter the C drive on the 1TB from that other computer, there, however, it seems like that's going to run into the same issue.

Again, will there be a conflict, and if so, what can I do to resolve it?


There should not be any conflict, as long as the boot drive is connected to the first disk in disk connector order. This is usually the disk you see in Disk Management with the name of "Disk 0".

Replacing the current boot disk with the other one, and ensuring that the current disk is unplugged, will keep it away from harm.

When you swap out the smaller disk and put back the current one, the BIOS will search the first connector and will boot whatever disk it find in there.

Ensure that the boot partition C is indeed Disk 0, since the boot disk can be distinct from the operating system disk. If unsure, you could add to the post a screenshot of Disk Management.

  • Thanks, that sounds helpful. It looks like the 500GB drive is already Disk 0. So that's good. screencast.com/t/7hF33tAg0Y The only other uncertainty I have how will the OS treat the "old" C partition when it is plugged back in, (because it has the "C" letter). Will it "re-letter it"? or just not assign a letter?
    – wayfarer
    Mar 7 '20 at 21:30
  • This is perhaps a problem. If the 500GB disk is the boot drive, and the OS is on the other disk, then installing Windows on it alone will cause it never to go back to booting the other disk. You should first work on making the OS disk into the boot disk, so booting will be from Disk 1. A good screenshot of Disk Management will help me comment on it.
    – harrymc
    Mar 8 '20 at 8:09
  • Thanks. Just to clarify, I do not need the PC to ever boot again from the 1TB Drive. In the future I will only boot from the 500GB drive. This is the disk management view screencast.com/t/fS2jvAr6zh and this is the general plan screencast.com/t/tyqjcVfjIF9g (it's about getting the DVD drive to work; long separate story)
    – wayfarer
    Mar 8 '20 at 19:14
  • The remaining mystery is what will happen when the "old" C partition on the 1TB suddenly reappears when I plug the 1TB back in.
    – wayfarer
    Mar 8 '20 at 19:48
  • If you reformat the 500GB disk, then whatever boot info that was on it will be erased and new one written. It should no longer boot the OS from the other disk, once you re-introduce it. In any case, this will be easy to verify.
    – harrymc
    Mar 8 '20 at 20:32

The answer in this case is that the 1TB turned out to be a M.2 NMVe on the Dell motherboard. When I reinstalled it, at first Disk Management did not recognize it. After I looked at in the F2 configuration and restarted, Disk Management said it had to be initialized. (See comment above).

If the 1TB SSD had been SATA, there might have been other options, however, that was not the case.

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