Creating a bootable Windows 10 USB drive on a Mac is a straightforward process that empowers users to install or repair Windows on Intel-based Macs or run Windows virtualized on Apple Silicon hardware. This guide walks you through the necessary steps using free, native macOS tools, ensuring a clean and reliable installation media without the need for third-party Windows software.
Understanding the Requirements
Before beginning, it is essential to verify your hardware and prepare the necessary components. You will need a Mac running macOS High Sierra or a later version, a USB flash drive with a minimum capacity of 16GB, and a valid Windows 10 ISO file downloaded directly from the Microsoft Software Download page. The USB drive will be completely erased during the creation process, so ensure any critical data is backed up beforehand.
Format the USB Drive
macOS requires the USB drive to be formatted in a specific scheme to be recognized as a bootable target for Windows. The GUID Partition Map (GUID) format is the standard for modern Macs, ensuring compatibility with the Boot Camp assistant and other disk utilities. Follow these steps to prepare the drive:
Insert the USB drive into an available port on your Mac.
Open Disk Utility, located in the Applications > Utilities folder.
Select the USB drive from the sidebar and navigate to the Erase tab.
Set the Format to "Mac OS Extended (Journaled)" or "APFS" and the Scheme to "GUID Partition Map."
Click Erase and confirm the operation to format the drive.
Mount the Windows ISO
Once the USB drive is formatted, you must mount the Windows 10 ISO image to make its contents accessible to the command line. Double-clicking the downloaded ISO file in Finder typically handles this automatically, creating a virtual drive on your desktop labeled "Windows 10 Install." This mounted volume contains the setup files required for the copying process. If the file does not mount, you may need to right-click the ISO and select Open to bypass security restrictions on Apple Silicon Macs.
Create the Bootable USB via Terminal
The core of this process relies on the diskutil and asr commands executed through the Terminal application. These tools provide the precision needed to write the ISO data directly to the USB drive. Follow these steps carefully, as entering the wrong disk identifier can lead to data loss on your internal drive.
Open Terminal from Applications > Utilities.
Type diskutil list and press Enter to display all connected drives.
Identify your USB drive by its size and note the identifier, usually /dev/disk2 or similar. Do not select the identifier for the internal disk (often /dev/disk0 ).
Unmount the drive by typing diskutil unmountDisk /dev/diskX (replacing X with your identifier) and press Enter.
Execute the write command: sudo asr restore --source /Volumes/Windows\ 10\ Install/ --target /dev/diskX --erase --noprompt .
Verify the Installation
After the command line process completes, the USB drive will contain the full Windows 10 installation files. The terminal will usually indicate a successful restore with a confirmation message. To ensure the media is bootable, you can check the drive in Finder; it will now be labeled "WININSTALL" or "Windows" depending on the ISO version. At this stage, the USB drive is ready to be used on a compatible Mac.
