How to Dual Boot Multiple HDD's

First and foremost to the Moderators if this isn't the right place I apologize. It seems right.

Here is what I have:

3 Internal HDD's: One is my main Windows 10 Installation and the other 2 are simple storage.

What I want:

Install Windows 7 to one of them and dual boot it with 10. I was hoping to avoid a total reinstall of Windows 10 by unplugging that and installing it to one of the blank HDD's I have. Then re-plugging Win10 back in and setting the main OS.

I am pretty sure I heard of this working before and I'd like to do it. If I REALLY wanted it I could reinstall both but damn....I don't want to.

Also my system is a UEFI type. (I am not entirely sure what that means but I know it has an impact on certain OS's)

Well son of a bitch. That's what I did. I unplugged the win10 and installed 7 for two reasons:

1) I heard installing an old OS on a separate drive/partition will override the boot loader and cause it to not load anything at all

2) it wouldn't let me install windows with he other hdds installed for some reason.

So windows 7 is currently installed but when I have my windows 10 HDD in it auto loads windows 10 and doesn't let me select an OS. File explorer does detect the 7 drive and I can access the files but as of this moment I have to unplug the Win 10 HDD to load 7.

So is there anything I can do to fix this without reinstalling? If I have to reinstall I will its still a bare bones install.

NavyLCDR said:

Let's say in Windows 10, the Windows 7 partition is E: drive. In a Command Prompt (Admin) ("Run as Administrator" Command Prompt) run:

bcdboot E:\Windows /d /addlast

Change the drive in red to match what Windows 7 gets assigned in your Windows 10.

You can change the default OS and the timeout on the boot tab of MSCONFIG.

Wow! Thank you so much NavyLCDR!

Also a shout out to everyone else here who replied :)

NavyLCDR said:

Amazingly easy, eh?

It added Windows 7 to the OS list but I am going to reboot and see if it actually gives me the option before I celebrate. Will edit with the reply.

NavyLCDR said:

Oh ye of little faith!

Now we have a major problem. When I did this it booted right into Windows 7 when it usually goes to Windows 10 first and no menu for selecting an OS. In Windows 7 I can access the W10 drive on E:/ files and all but it will not boot into Win10. When it did Windows 7 insisted on a disk check for "Consistency" for the Win10 Drive. So I let it do it's thing then it did something I've never seen before

"Deleting extended attribute set due to the presence of reparse point in file XXXXXX" For hundreds of thousands of files.



This went on for like 5 minutes so I got irritated and did something I probably shouldn't have done which was hit the rest button on my PC. I rebooted into Win7 again and skipped the checks. Got to my desktop and I could still access my Win10 drive. Windows 10 is also now gone from the OS list.

When I rebooted my PC I hit F11 for the boot menu and selected the Windows 10 Drive. It said something about inserting bootable media. I didn't take a screenshot of that. I plugged in my Windows 10 USB and booted from that and selected repair errors that prevent startup. It couldn't fix the errors so I chose to Recover using a restore point. It gave me an error box saying something like "Restart and select windows version you want to repair" Even after I unplugged my Windows 7 drive it still said this."

This all happened after I entered that command you told me to input. And yes Windows 7 happened to be E:/

So for a super short version:

I did that command in command prompt. Windows 7 DID list in the OS list on Windows 10. I rebooted and it went into Windows 7 immediately. Did a disk check stating "Deleting extended attribute set due to the presence of reparse point in file XXXXXX" Windows 7 can access the Windows 10 Files no problem in File Explorer. Cannot repair it with my USB Win10. Cannot boot into it or repair even with Windows 7 unplugged.