Can I Dual Boot After The Fact?

If anyone thinks they are important, here are the specs for my machine. Skip them if you want. I have never purchased a computer built by someone else. They always seemed to be clunky and they put in what they want to sell you. I just like my builds much better than someone else’s.
P/S: Antec Edge 650 (new as of a month ago)
Mainboard: Intel DP67BG
Processor: Intel i5 Quad Core 2320 3.0 Ghz
Memory: Kingston DDR3 – 16 Gb
Graphics: NVIDIA GeForce GT 730
Hard Discs:
Drive C: Western Digital 650 Gb 7200
Drive E: Western Digital 2 Tb 7200
Drive G: Seagate 150 Gb
O/S: Windows 7 Ultimate x64
Of course various peripherals that I’m sure are not germane to my post


Okay, here is a sort of different W10 story in that it installed very smoothly and even ran very nicely (if you like that kind of interface) but I didn’t want to replace my O/S. I just wanted to have 10 so I can play around with it before it gets to the point that it’s the only thing available at which time I’ll have to switch.


I really love my 7 x64. It is by far the most stable operating system I’ve ever used and I go back to before Windows existed. Bought Windows 10 Pro and decided to do a clean install on my back-up Seagate that normally just sits there doing nothing. (I do backup my data but keep everything on the 2 Tb drive.)


So I unplugged both W/D hard discs and booted via the Windows 10 Pro DVD. As I said, it went very smoothly and I opened the hood and trunk and nosed around a bit, took it for some very easy road tests and decided to put it away for the day. I booted down, plugged the other two drives back in and waited for the fireworks to begin. I knew the BIOS was going to shit an IC because my C drive has always been my boot drive and for the O/S and not much else. I like to keep it as clean as possible. But I also know that I just finished installing Windows 10 on a freshly formatted HDD. So I knew a conundrum would take place and it did.


I got a black screen with the message that my Windows system has had some files replaced or some non-descript hardware possibly was changed which rendered the boot process broken.


Not a problem since I did not intend to be working on 10 for some time and I know how to revive 7 Ultimate since I tear it up a lot and I’m always pushing the limit on what it’s made of. Just to make sure I got back to my regular work soon enough, I unplugged the G drive which is now the Windows 10 drive and kept my two W/D drives plugged in, and launched right into my desktop.


I guess I said all that to say all this…and maybe I will have to clean and reinstall 10 but I’d like to find out if I can dual boot at this stage. Mind you, when I installed 10, my machine knew nothing of another O/S or other drives, applications etc. So is it possible to dual boot after both O/S have been installed on separate drives?


I am very hesitant to install 10 with my other two drives still connected because about a year ago when I put the 2 Tb drive in, the boot files were scattered over two discs which made it hard to get it back to all on my C drive. Long story. I got very acquainted with the BCD at that time (thank you 7 forums and their members) and got it straightened out, but don’t want to mow that yard again.
Any advice or speculation would be appreciated.
Sorry for the length of the post. I’ve never been accused of being succinct.

You can connect your Windows 10 disk again and then enter BIOS and make sure your Windows 7 disk is first in hard disk priority, BOOT section. If your Windows 7 disk is first in the list, your system will try to boot from it first and you should see the Windows 7 desktop without having to do anything on your part. Then you have to use EasyBCD (so as not to mess with bcdedit) and add a boot entry for Windows 10. In theory this is possible, although I have read in another post that you can only add a boot entry in Windows 10 for 7 not in 7 for 10. However, I would try it. If this is not possible, then you have to change the hard disk priority to make Windows 10 first, boot into Windows 10 and use EasyBCD to add an entry for Windows 7. You can also make Windows 7 default. Either way, you should be able to dual-boot Windows 7 and 10 by simply setting the right hard disk priority and adding a new boot entry in Windows Boot Loader.