Create a bootable Windows 10 installation USB drive on a Mac

March 24, 2021

This is a guide to create bootable Windows 10 installation USB drive on a Mac. Normally I would use the Microsoft Media Creation Tool on a Windows PC, but at that time I only had access to my Macbook.

I first tried balenaEtcher which I normally use to create my Raspberry Pi SD cards and Linux installation drives, but this tool failed to read the downloaded Windows ISO file.

Download Windows 10 ISO image

First of alle we need a up-to-date Windows 10 ISO file. Microsoft provides an easy way to download the Windows 10 ISO file. Just choose the correct version on the official download site.

Prepare USB drive

During the download the USB drive can already be prepared with the correct file system. Connect the USB drive to your Mac and open the Disk Utility program. In the tool select your USB device and click on “Erase”. Name the device WININSTALL (the name will be used later) and select the FAT filesystem and Master boot record (MBR) partition schema.

Format USB drive

⚠️ Keep in mind that all data of the USB device will be deleted!

Install homebrew

Now we need some utilities to modify the installation files. These can be downloaded by using the Homebrew package manager. If you haven’t already installed homebrew on your Mac you can follow the instructions here.

Install wimlib

After the homebrew installation, it is just one command to install the wimlib tools.

brew install wimlib

Copy all smaller files to the USB drive

After the download of the ISO is completed, copy all files except the install.wim to new formatted and connected USB drive. With the rsync command below this all happens at once. Please change the name of the mounted ISO file (in this example CCCOMA_X64FRE_DE-DE_DV9) to your version. It depends on the choosen version and language on the download page.

rsync -avh --progress --exclude=sources/install.wim /Volumes/CCCOMA_X64FRE_DE-DE_DV9/ /Volumes/WININSTALL

Split the install.wim file

Because of the 4GB file size limit of the FAT file system it is required to split the larger install.wim file into separate parts. This can be performed with the previously installed wimlib-imagex command. As with the rsync commmand, please change name name of the mounted ISO and USB drive to your values.

wimlib-imagex split /Volumes/CCCOMA_X64FRE_DE-DE_DV9/sources/install.wim /Volumes/WININSTALL/sources/install.swm 3500

After the command finished successfully the drive can be removed and used to install Windows 10 on a PC.

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