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Once all deleted, create a new partition.Be certain to not delete any data drives you want to keep (you should have removed them). If any partitions exist on the drive, delete them here.Follow the Windows 10 installation process as you would normally but one you reach the partitioning step.Power on the PC and place the Windows 10 install DVD into the DVD drive.Attach the disk drive for use on your Mac Pro in to the PC SATA cable and power connector.
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Removing the drives of the installed PC will save you from deleting anything by mistake. I strongly suggest that you remove any installed data drives in the PC and take note of any BIOS setting changes so that once we're done with this step, you can put all settings and hardware back to their original state. You may need to make changes to the BIOS settings and each motherboard has its own configuration which is beyond the scope of this article.
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Next we'll need to start Windows 10 installation process from the Legacy BIOS enabled PC. That's all the software prep we'll need to do.
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We're going to trick Windows 10 to use the older legacy BIOS booting and to also use partitioning called MBR rather than the newer EUFI and GPT technologies. I know many purists will scoff at this point since a Mac Pro uses UEFI for booting but since we will be dual booting and macOS Mojave on Mac Pros don't play nicely when Windows 10 is using what's called a GPT partition for UEFI booting, we'll completely bypass the booting problems that come with those technologies. The next thing you'll need is access to an older PC or a PC with a motherboard that allows you to set the UEFI boot to Legacy BIOS boot.
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