Do I have to reinstall UEFI Windows in Legacy to dual boot with another Windows in Legacy?

Question

I currently have Windows 10 in UEFI installed on my laptop and I can't install Windows 7. I want both OS in dual boot but I can't get the boot USB to work properly in UEFI.

I then proceed to disable UEFI in the BIOS which then let me boot from the USB drive but now I can't access Windows 10. I realize that I either have to choose Legacy or UEFI and the only way for me to install any OS is in Legacy (as my thumb drive won't boot in UEFI).

So my question is: If I want to dual boot and access both OSs, do I need to reinstall the current Windows 10 OS UEFI in Legacy? Is there any other way to change it from UEFI to Legacy?

Answer 1

Instead of re-installing Windows 10 in BIOS/CSM/legacy mode, I recommend you install Windows 7 in EFI/UEFI mode. I know you say this can't be done, but you're wrong -- it can be done. Many Windows 7 media are just created in a way that makes it hard to boot them in EFI mode. There are lots of Web pages that cover how to do this. A Web search turned up these, just to start with:

• http://www.sevenforums.com/tutorials/186875-uefi-unified-extensible-firmware-interface-install-windows-7-a.html
• https://technet.microsoft.com/en-us/library/hh290675%28v=ws.10%29.aspx
• Clean install of Windows 7 Pro 64-bit on a UEFI laptop with GPT partition?
• https://rufus.akeo.ie/

The first three of those are to tutorials or discussions about the subject, but the last is to a tool that can help you create a USB flash drive version of the Windows installer that should boot in EFI mode.

Installing Windows 7 in EFI mode has the advantage that you won't have to mess with your Windows 10 installation, so it should be easier and less likely to create new problems. There are also a number of (mostly minor) advantages to EFI-mode booting, such as Secure Boot support. (To my surprise, when I installed Windows 7 recently, it worked fine with Secure Boot enabled.) That said, system-to-system variability is huge, and if you're familiar with various tricks to BIOS-mode booting, most of those won't apply to EFI-mode booting, so you may have a bigger learning curve if you go with the EFI-mode option.

Answer 2

NO.

As long as you have Windows 10 in EUFI, you can install Windows 7 in legacy. On the BIOS settings, you will need to find an option that says enable legacy-rom or something in that area. With the advent of Windows 10, you can also boot from Windows 10, enter credentials, then go to settings> Update and Security > Recovery > Advanced startup > USB device. You might also see an option saying EUFI USB DEVICE but that, as you said, will not work. This will restart and boot from the USB.

I suggest searching up "How to enable LEGACY compatibility on X laptops" or something in that zone when X is your manufacturer.

Answer 3

Short Answer: Yes.

Unless you wish to enable legacy boot support in BIOS (Bios switch method), both instances will need to be in legacy (aka UEFI-CSM) or UEFI