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Guide: Multibooting UEFI on Separate Drives

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If I am understanding you correctly, you want to have Mojave on a new drive you installed and you want to then install Win10 on the existing drive with Mojave on it.

Clone Samsung 970 to other drive.
Disconnect Mac OS drive or disable SATA port in UEFI/BIOS.
Boot Windows 10 install media. At the screen which asks you to select a drive/partition to install on, select each partition and click delete until

hit shift+F10 to open a command prompt.
type the following lines, hitting enter at end of each line
diskpart
list disk

//determine which drive is the one you want if more than one drive is connected. Be very careful here as you will destroy all data on the drive you select, especially if you use clean all which zeros the drive. Do not use clean all very often on a SSD as it shortens the life of the SSD. You will be able to tell the USB by the smaller size//
say your drive is disk 0, type

select disk 0
clean
exit
exit

this leaves your drive with all unallocated space. Select this unallocated space to install Win10 and hit continue/install button. Win10 installer will take it from there.
not exactly, I want to keep mojave in my samsung 970 pro "it is already installed and working perfectly", I have another Samsung ssd drive that is where I want to install windows, thank you very much for your help and answer
 
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If Clover will boot it, or if you are using the Fxx key to select the Win drive to boot, do not bother.
Earlier Clover versions often had problems with an EFI partition that is not the first partition on the drive. Win 10 install puts WinRe Tools on the first partition, then the EFI partition, but will leave an existing EFI partition as first if it already exists and use it - hence the instruction to create the EFI partition using the Mac Disk Utility. For those who are handy with Windows command line, an elevated prompt at the Win10 install screen and using diskpart to format the drive and create the EFI partition would work as well, but for most, the Mac OS disk utility route is easiest.
Thanks. I think the Clover version on my USB stick is approx 1 year old and it boots Windows fine from existing NVME so I won't have to wipe and re-do.
 
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Another potentially dumb question but why not just only connect the drive you want to install the OS to and then disconnect drive and do next and so on. Then plug all 3 in and select the MacOS drive as the boot drive so Clover is the bootloader and does the job? Is there something missing here? I would assume this would also help with the issue of Windows getting over-excited and over-writing the EFI priorities and removing Clover (which happens all the time on my dual boot system without some interventions!).
 

Going Bald

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Another potentially dumb question but why not just only connect the drive you want to install the OS to and then disconnect drive and do next and so on. Then plug all 3 in and select the MacOS drive as the boot drive so Clover is the bootloader and does the job? Is there something missing here? I would assume this would also help with the issue of Windows getting over-excited and over-writing the EFI priorities and removing Clover (which happens all the time on my dual boot system without some interventions!).
Precisely why I recommend having only target drive connected - either disconnect or disable ports for other drives in UEFI/BIOS for installation and reconnect/re-enable when installations are finished. This prevents all kinds of hassle between OS's for resources.
 
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Hi,

I had successfully installed high Sierra on My Hp 8300 HDD using trs96 High Sierra Install guide. Now i have bought a 180 GB SSD and want to dual boot with windows. My Mac OS High Sierra should be on SSD and my windows 10 should be on HDD.

After reading this guide, i have understood that to multiboot windows and mac on separate drives, i can follow these steps.
  1. Prepare Bootable Usb's, One for high sierra and one for windows.
  2. Instal High Sierra on SSD using This Guide (should i disconnect HDD during this step?)
  3. Install Windows 10 on HDD using these instructions (should i disconnect SSD during this step?)
  4. For Win10:
    Connect a drive, insert OS X Install USB, boot the system and at the POST hit the Function hotkey that allows you to select a boot device. Select the OS X Install USB. At the installation screen, select Utilities->Disk Utility and format the drive single partition GUID/Mac OS Extended (Journaled). When done, exit Disk Utility. Quit the OS X installer.
    Remove the OS X Install USB and insert the Win10 USB, boot the system and at the POST hit the Function hotkey that allows you to select a boot device.
    Windows shows up as USB: Win10Installer (or whatever you named the USB) and as UEFI USB: Win10Installer.
    Select the UEFI USB: Win10Installer and boot the system.
    At the installation screen, select Custom Install. At the next screen select the OS X partition and delete it - do not delete the EFI partition. With the resulting free space hi-lited, install Windows to the space. The installer will create and format the partitions for you. When finished, update and install your 3rd party apps and security suite. Reboot to BIOS/UEFI and disable CSM. Save&exit, continue boot to desktop. Shut down, disconnect the drive.
That's it? Following these steps. i would be able to successfully multiboot? Is there anything that i am missing ?

In the trs 96 High Sierra Install Guide, there is a discussion about APFS conversion. Can you tell me what it is and why or why not one should do it. I am experience slow boot times on high sierra on my HDD. Does that link to APFS ?

And what does that mean ?
Note that CSM must be enabled for the installation process.

Thank you very much.
 

Going Bald

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Hi,

I had successfully installed high Sierra on My Hp 8300 HDD using trs96 High Sierra Install guide. Now i have bought a 180 GB SSD and want to dual boot with windows. My Mac OS High Sierra should be on SSD and my windows 10 should be on HDD.

After reading this guide, i have understood that to multiboot windows and mac on separate drives, i can follow these steps.
  1. Prepare Bootable Usb's, One for high sierra and one for windows.
  2. Instal High Sierra on SSD using This Guide (should i disconnect HDD during this step?)
  3. Install Windows 10 on HDD using these instructions (should i disconnect SSD during this step?)
That's it? Following these steps. i would be able to successfully multiboot? Is there anything that i am missing ?

In the trs 96 High Sierra Install Guide, there is a discussion about APFS conversion. Can you tell me what it is and why or why not one should do it. I am experience slow boot times on high sierra on my HDD. Does that link to APFS ?

And what does that mean ?



Thank you very much.
Ivy bridge hardware may or may not be set up in UEFI/BIOS to be UEFI only or Legacy only.
Double check your BIOS/UEFI settings
Boot to HS, right click on the drive and select Get Info - check the format - is it HFS+ (Mac OS Extended (Journaled) or APFS?
 
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Ivy bridge hardware may or may not be set up in UEFI/BIOS to be UEFI only or Legacy only.
Double check your BIOS/UEFI settings
Boot to HS, right click on the drive and select Get Info - check the format - is it HFS+ (Mac OS Extended (Journaled) or APFS?
I went to disk utility and right clicked on disk. It says

File system : Mac OS Extended (Journaled)

As seen in screen shot
 

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Going Bald

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I went to disk utility and right clicked on disk. It says

File system : Mac OS Extended (Journaled)

As seen in screen shot
OK, you have HFS+ format instead of the new APFS (Apple File System), so no problems there.
CSM is Compatibility Support Module and allows Legacy booting on UEFI based systems.
Since the Win10 installer is Legacy mode, CSM must be enabled to allow it to run. Look under the Boot tab in the BIOS for the boot mode setting. You should see Legacy, UEFI and Legacy/UEFI options. Select the Legacy/UEFI, save&exit and continue boot. Use the function hotkey to select boot device, select the Win10 installer and follow the prompts. When asked to select a partition to install Win10, select the partition you created for it, delete it to free space and hit install.
Post results with pics if this does not work.
 
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OK, you have HFS+ format instead of the new APFS (Apple File System), so no problems there.
CSM is Compatibility Support Module and allows Legacy booting on UEFI based systems.
Since the Win10 installer is Legacy mode, CSM must be enabled to allow it to run. Look under the Boot tab in the BIOS for the boot mode setting. You should see Legacy, UEFI and Legacy/UEFI options. Select the Legacy/UEFI, save&exit and continue boot. Use the function hotkey to select boot device, select the Win10 installer and follow the prompts. When asked to select a partition to install Win10, select the partition you created for it, delete it to free space and hit install.
Post results with pics if this does not work.
Ok. i will set it to Legacy/UEFI in BIOS.

Currently I have high sierra on My HDD. so first, i should install High Sierra on my SSD. Then Install windows 10 on my HDD?

And should i do the APFS conversion that is discussed in trs96 High Sierra Install guide ?
 

Going Bald

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Ok. i will set it to Legacy/UEFI in BIOS.

Currently I have high sierra on My HDD. so first, i should install High Sierra on my SSD. Then Install windows 10 on my HDD?

And should i do the APFS conversion that is discussed in trs96 High Sierra Install guide ?
Step back a moment - I was under the impression you were installing on same drive as Mac OS.
If installing Win10 on a new SSD, if you want to install Win10 UEFI mode for booting on a UEFI system you will first have to convert the MBR format to GPT. The easiest way to do this is to format it with the Mac OS Disk Utility. Just format the SSD with a single partition as if you were going to install Mac OS. Reboot to the Win10 installer, select the largest partition, delete it, and click install. Win10 should have no problems installing itself.
 
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