Windows Installation

Creating an installation disk

Mac OS

The flash drive should have a capacity of at least 10 Gb.

Identify the drive where the USB flash drive is mounted

Insert the flash drive on a Mac.

Open a terminal window.

$ diskutil list

This should display all the disks currently mounted on the system along with the USB flash drive. Take note of the IDENTIFIER value, e.g. /dev/disk2.

Format the USB flash drive

$ diskutil eraseDisk MS-DOS "WIN10INST" MBR /dev/disk2

• MS-DOS is the filesystem
• "WIN10INST" will be the name of the drive. This can be any arbitrary name.
• GPT is the partition type. "GPT" is necessary for PCS that boot in UEFI mode.
• /dev/disk2 is the identifier of the USB drive. This identifier could be a different value depending on the Mac.

One guide for creating the installation flash drive recommended using the GPT option in place of MBR when formatting the drive. Using the GPT option caused many errors and ultimately did not create a drive that could be used to successfully install Windows. It would boot, and the Windows installation would start, but the installation would fail at various points with a variety of error messages.

After using the GPT option there would be two partition options for booting from the disk. With the MBR option, there is only one partition option for booting from the disk.

MBR stands for Master Boot Record and GPT stands for GUID Partition Table.

Mount the Windows ISO

$ hdiutil mount ~/Downloads/software/Win10_20H2_v2_English_x64.iso

The path to the Windows ISO file can be different, of course. It would be wherever the file was downloaded.

Copy the Windows 10 ISO to the USB flash drive

Mac OS doesn't read NTFS filesystem natively. This is why the USB drive is formatted using MS-DOS. However some files (e.g. install.vim) are too large to copy to MS-DOS. They need to be split and then copied over.

First copy all the files except the ones that are too large:

$ rsync -vha --exclude=sources/install.wim /Volumes/CCCOMA_X64FRE_EN-US_DV9/* /Volumes/WIN10INST

Again, the names of the volumes may be slightly different.

Now copy files that are over 4Gb. This requires wimlib which can be installed with homebrew.

$ brew install wimlib

Split the file(s) into 3800Mb parts in order to accommodate the MS-DOS limits.

wimlib-imagex split /Volumes/CCCOMA_X64FRE_EN-US_DV9/sources/install.wim /Volumes/WIN10/sources/install.swm 3800

Again, the paths to the source and destination directories may be slightly different.

Eject the USB drive

The installation drive is ready to be used. Power off the PC. Insert the USB drive in the PC. Load the BIOS on the PC and select the USB drive as the primary boot drive.

Troubleshooting

Windows installer complains that it can't install from or on a particular drive

Possible cause

The Windows installer can't boot from EFI/UEFI drives.

Solution

Look at the boot order in the BIOS. The primary boot drive should not start with UEFI or EFI. If the USB drive starts with UEFI, the installation files must be copied to a drive (SATA) that does not start with UEFI and the installer must be booted off that drive.

Can't create a new partition or locate an existing one

Error

Error: "We couldn't create a new partition or locate an existing one." on the Where do you want to install Windows? prompt.

Cause

The installer is having difficulty installing from the flash drive.

Solution

Create a partition on the hard drive and copy the Windows install files there.

• Plug the flash drive with the installer on it into an USB port.
• Boot from the flash drive.
• At the Where do you want to install Windows? screen displaying the error message press Shift + F10 to get a command prompt.

> diskpart
> list disk
> select disk 0
> clean
> create partition primary size=5000
> format fs=ntfs quick
> assign
> active
> list volume
> exit
> cd c: 
> xcopy e: c:/e/h/k
> exit

• select disk 0 selects the hard drive onto which the installation files will be copied.
• create partition makes a partition on the hard drive where the installation files can be copied.
• assign assigns a drive letter to the new partition.
• xcopy copies the installation file from the USB drive to the hard drive.
• The last exit closes the command prompt window.

• After closing the command prompt, remove the USB flash drive and click the X button at the top right of the Windows installation window to close the current installation and reboot the computer.
  • Without a mouse, click Esc, the confirm to quit the installation. If this leads back to the first window of the Windows installation, click Esc again, and again confirm that the installation will be canceled.
• The computer should now boot from the hard drive and the installation will use the files from the new partition.