MP 1,1-5,1 OpenCore Multi-Boot w/Windows 10 and Mojave on 5,1 cMP?

[riven2000]

My system is:
4,1 cMP flashed to 5,1
Single X5690 CPU
48GB RAM
Radeon RX 580 8GB
Mojave with OpenCore
Windows 10

I've looked all over here for the best way (that won't brick the machine) to install Windows 10 with OC, so I can use BootLoader. It seems like that can only happen with a UEFI install, but this supposedly hoses the BootROM. Is there a safe way to do this that I'm missing, or do I have to do a legacy install w/no BootLoader?

 

[startergo]

First of all you don't need a boot loader to boot Mojave on cMP. No need for Open Core unless you need a hardware acceleration. Safest way to install Windows to cMP is in Legacy mode. You can boot that Windows from the Apple Boot Picker menu or from the Startup Disk menu. To boot to macOS from Windows you can use the Bootcamp assistant in Windows. Here you have some threads for installing Windows in Legacy mode:

Bare Metal Windows on cMP

PART 1 of 3 This is a guide to installing Windows 10 on Classic Mac Pros without the Boot Camp Assistant. This is one of many ways to implement such a "Bare Metal" setup but is a straightforward method. This guide is for installing Legacy Windows, as opposed to UEFI Windows, but can also be...

forums.macrumors.com

Installing Windows 10 in Legacy/BIOS mode in cMP with Boot Camp Assistant

Installing Windows 10 in Legacy/Bios mode in classic Mac Pro is easy. You will have to use a modified Bootcamp assistant, which I attached to this post or make your own using this guide. The installation has been tested on High Sierra partition with HFS+ partitioning scheme. The only limitation...

forums.macrumors.com

 

[riven2000]

Thanks. I know about Mojave not needing OC, but I understand there isn't any Startup Manager when running an unflashed RX 580 card. So the main thing I want OC for is BootLoader between Mojave and Windows.

 

[haralds]

From what I understand OC is not compatible with Mojave.

 

[prefuse07]

Thanks. I know about Mojave not needing OC, but I understand there isn't any Startup Manager when running an unflashed RX 580 card. So the main thing I want OC for is BootLoader between Mojave and Windows.

I believe you can get the bootpicker/startup manager by holding down the Option key during the chime. Then you can choose which disk/OS you want to boot into:

In case you still do want to try Open Core -- I suggest giving THIS a read, then pick up his latest config and give it a shot.

With the above, I would also recommend installing Windows in UEFI mode as opposed to Legacy.

Lastly, for help with Windows and Open Core, check THIS out -- scroll down to "Appendix: Windows" and follow the instructions.

Update: Just re-read your OP, I must've missed this, but it looks like you ALREADY have OC running?

In that case, as I mentioned above just follow THESE INSTRUCTIONS (scroll down to "Appendix: Windows" and follow the instructions) -- you will want to install Windows in UEFI mode, NOT Legacy.

Helpful Tip: Once you do the majority of the work required (i.e. ExFatDxeLegacy.efi, etc...), it's pretty simple. You just connect your flash drive with Windows 10 on it, and from within the OC bootpicker you select "Install Windows 10" and then let it go thru the process. Once it's finished, again from the OC boot picker, select Windows and voila.

 

[Dayo]

UEFI Windows is perfectly fine as long as you (or anyone else accessing your Mac) remember that when you hold the Option key down on boot and see the UEFI Windows option (or see the option to run UEFI Windows virtually anywhere but in the OpenCore picker), that you must never ever, deliberately or mistakenly, select that option.

Equivalent to having a fully grown Bengal Tiger tethered to a tree in your back garden. This, as everyone knows, is perfectly safe (given the sturdy chain in use) as long as you clearly mark the "Kill Zone" out and you tell the kids not to stray there when playing outside.

Some prefer to use Legacy Windows to avoid such kill zones altogether.

 

[startergo]

Thanks. I know about Mojave not needing OC, but I understand there isn't any Startup Manager when running an unflashed RX 580 card. So the main thing I want OC for is BootLoader between Mojave and Windows.

You can patch your firmware to enable native Apple boot picker nowadays. There is a thread about it.
But like I said you don't need a bootpicker to boot to Windows 10. You can do it through the startup disk.

 

[riven2000]

UEFI Windows is perfectly fine as long as you (or anyone else accessing your Mac) remember that when you hold the Option key down on boot and see the UEFI Windows option (or see the option to run UEFI Windows virtually anywhere but in the OpenCore picker), that you must never ever, deliberately or mistakenly, select that option.

Equivalent to having a fully grown Bengal Tiger tethered to a tree in your back garden. This, as everyone knows, is perfectly safe (given the sturdy chain in use) as long as you clearly mark the "Kill Zone" out and you tell the kids not to stray there when playing outside.

Some prefer to use Legacy Windows to avoid such kill zones altogether.

See, this is the kind of question I was asking, and the answer I was looking for - Is it _ever_ ok to install UEFI Windows on a cMP, using one of the many methods we have here, or is there still the risk of killing the BootROM. Apparently there is, so I will take OC off and stick with legacy dual boot. And BTW, another awesome metaphor with the tiger! THANK YOU MUCHLY!!!

 

[startergo]

See, this is the kind of question I was asking, and the answer I was looking for - Is it _ever_ ok to install UEFI Windows on a cMP, using one of the many methods we have here, or is there still the risk of killing the BootROM. Apparently there is, so I will take OC off and stick with legacy dual boot. And BTW, another awesome metaphor with the tiger! THANK YOU MUCHLY!!!

You don’t need to remove OC. OC does not hurt your firmware UEFI Windows may.

 

[Dayo]

the risk of killing the BootROM.

There is always the risk with UEFI Windows but whether this becomes an issue or not depends on how you handle it. Every time you get behind the wheel of your car, you are taking a risk. Once you are aware of risks however, you just need to act accordingly. Avoidance/elimination is not the only option and we typically manage risks.

In your case however, since you only want to run Mojave and Windows, then, as @startergo pointed out, you do not need OpenCore and should stick with Legacy Windows (natively supported by your Mac unlike UEFI Windows). In other words best to avoid/eliminate the risk in your case since there is no reason why you have to deal with managing it.

If your GPU supports showing the native boot screen, you can use this as your boot manager for selecting between Mojave and Windows. You can access the native boot screen by always pressing the OPTION key whenever you need Windows or set your Mac to always show this screen by entering sudo nvram manufacturing-enter-picker=true && sudo reboot in Terminal. In both cases, your GPU needs to have the required support.

If your GPU does not support showing the native boot screen, then you can either flash the GPU or firmware yourself if you have the chops for managing such, pay someone to do it for you, or use a third party boot manager such as RefindPlus (which incidentally, offers UEFI Windows protection).

You can keep your OpenCore setup for flexibility of installing other Mac OS versions down the line but if you are sure you will be staying with Mojave for the foreseeable future, you might as well ditch OpenCore, go native and revisit OpenCore if/when you actually need it.

 

[riven2000]

Yeah, in my case it's all about the configuration. I do plan to stick with Mojave as most apps I use are 32-bit. But this is with an unflashed RX 580 (so no native Startup Manager) so I need another, safe, method of switching OSs. That's all it really boils down to. I don't want to have to remember to use OC this way and not that way, and make a fatal mistake if I forget, so I think you're right about ditching OC and using RefindPlus for OS switching.

 

[riven2000]

Yeah, in my case it's all about the configuration. I do plan to stick with Mojave as most apps I use are 32-bit. But this is with an unflashed RX 580 (so no native Startup Manager) so I need another, safe, method of switching OSs. That's all it really boils down to. I don't want to have to remember to boot Windows this way and not that way, and make a fatal mistake if I forget, so I think you're right about ditching OC and using RefindPlus for OS switching.

 

[Macschrauber]

Before you take on with windows installs you can backup your bootrom and check for certificates with my tool.

In case you get certs you can flash back the backup.

https://forums.macrumors.com/threads/healthy-nvram-normal-behaviour-on-4-1-5-1-machines.2333460/post-32055801