How to Dualboot macOS/Win from the same SSD (GPT) without UEFI

[Injury]

I've started this thread to help someone who's trying to make dualboot of macOS and Win from the same drive, while using older mobo with bios instead of uefi. I've lost a couple of days trying to find solution for myself and if there was a thread like this somewhere, it would save lot of time for me. As far as I can read from your profile, you're using Asus P9D WS mobo, which features UEFI so you aren't affected by this problem

You can assume that's the situation, but that doesn't mean that's what's going on.

I still to this day am not able to UEFI boot off of my OS drive for OS X/macOS. Which is why when I finally figured out how to multi-boot off a single drive I made 3 guides of my own: UEFI, Legacy, and Hybrid, just in case if I were to run into the same dreadful issue in the future I would be ready for it.

and I can't understand what's your motivation to dig into this?

To help out?

Maybe just to kill some time by trying to explain to me that I'm talking nonsense here?

Well, you did state incorrect information, which is why I tried correcting that in hopes it would help your situation a bit.

 

[geter712]

I've finally managed to get rid of booting from USB, every time I need to get into Windows. I've copied the whole bootable partition from USB to another internal HDD, even managed to resize it from 1gb to 100mb. Now I'm able to choose boot drive from bios menu. If I choose SSD, macOS will boot and if I choose another internal hdd, I get into Windows 10 (which also loads from SSD). May be a little bit strange setup, but it works perfectly. Bootable partition for Windows is stored to separate HDD but the rest of its space is available for storage, which I'm gonna partition using exFat (in order to be able to read/write from both OS).

Here's how it looks. Small green partition is bootable for Win10 while the rest of its disk is storage.