Dual boot Win7 and Win10?

If you remove the hd put we one in and install 7 then put 10 back in as well you should be able to boot by selecting drive in the BIOS or you could run 7 as a virtual machine

Been many years since I also dual booted XP and Win 7. Does this help? Best Dual Boot Manager software for Windows 10/8/7 PC | H2S Media

RoWin7, I recently completed a video that you might find helpful. You don't have to follow the same technique, but some of the background info may be useful to you in understanding the issues and deciding how you want to do it.

The first thing you'll want to do is settle on Legacy boot or UEFI. You could have one Legacy boot disk and one UEFI disk, but it would be a hassle to have to go into your BIOS and reset the boot mode and Secure Boot every time before switching to the other OS. So I recommend choosing one or the other and having both OSes boot the same way.

If you settle on Legacy boot, you can put Win7 [System+Boot] on one disk and Win10 [System+Boot] on the other, and choose the boot disk from the BIOS boot menu. Both OSes would be completely independent, and you could remove either disk and the other would still boot. Note from my video that if you use Macrium Reflect it's trivial to convert Win10 from UEFI boot to Legacy boot.

If you settle on UEFI boot, you'd need to install Win7 as UEFI boot on one disk and keep Win10 as is, on the other disk. Again, both disks would be completely independent. Instead of choosing the boot disk from the BIOS boot menu, you'd choose the OS. That means you'll need to make sure the second OS is added to the BIOS boot menu. I don't have much experience doing that so don't know what pitfalls there may be, but I don't think it's hard -- certainly no harder than getting Win7 installed in UEFI mode in the first place.

Personally, I don't understand the reluctance to put two OS partitions on the same disk, but if you're against that it's certainly possible to do it the way you want. All the various possibilities are just a matter of how much effort you're willing to put into setting it up.

For comparison, if you were to follow the technique in my video, you would:

• make a backup image of the Win10 system (at least the OS partition, but no harm imaging the whole disk);
• switch BIOS to Legacy boot and install Win7, leaving unallocated space for Win10;
• restore Win10 OS partition to unallocated space;
• use Macrium's "Fix Windows Boot Problems" tool to rebuild the BCD.

(This assumes the boot disk is no more than 2 TB and the computer supports Legacy boot.)

Thereafter, you'd choose the OS from the BCD boot menu, not the BIOS. You don't have to hassle with getting Win7 installed in UEFI, and you don't have to hassle with setting up a multi-boot manager because Macrium does that for you automatically. However, the two OSes would be on the same disk.

SIW2 said:

Nice video, Dan. A bit complicated for beginners.

That's okay, since it isn't aimed at beginners. I make videos and tutorials aimed at people who want to understand how something works. If all somebody wants is for someone to just tell them the steps and skip the context, there are plenty of HOW-TOs on the Internet for just about any subject. No need for me to add to the Internet Noise.

Unfortunately, too many HOW-TOs are by self-promoted "experts" who stumbled across something and now they're touting it as "THE BEST" or "THE RIGHT WAY" to do something. Many are at best misleading, and ocassionally some are just plain wrong.

Just look at the number of people who will vociferously argue that it's impossible to have more than four partitions on an MBR disk; or Windows can only be installed on a primary partition; or Win 7 requires a System Reserved partition; or Win 10 requires UEFI/GPT; or that MBR partitions are different from GPT partitions; or that MBR should be avoided whenever possible (just look at the forum posts from people who go out of their way attempting to convert Win7 to UEFI mode when there's no reason to do so).

Each takes a grain of half-truth out of context and morphs it into some kind of immutable "fact". Real experts may know better, but on the Internet how can others tell the difference? That's why I try to add background explanations, so help seekers have some basis for making up their own minds.

If one isn't interested in understanding and only wants a step-by-step list to follow, there are plenty of HOW-TOs that may get you by. But when the result doesn't come out the way you wanted, you can either flail about randomly trying other HOW-TOs hoping something will suddenly work by happenstance, or you can try to understand what went wrong.

Note: just to be absolutely clear, none of this is to be construed as commentary on any poster in this thread. It's offered simply to explain how I compose forum posts or my own videos and tutorials.

BTW, the impetus for that particular video was to present an alternative way to create and maintain a multi-boot system. Combined with what a viewer may already know about multi-booting, looking at it from a different perspective may help the viewer gain a better grasp of the whole subject, regardless of how they choose to do it for themselves. That's the hope, anyway.