Downloading and Creating a Windows 10 Bootable USB on Mac OS X


As the Windows 10 Media Creation Tool is an application it cannot run on Mac OS. The Windows 10 Software Download Page will therefore display as direct download links:

You will prompted to select your "Edition". This actually displays the version as the ISO is a multi-edition ISO which covers all OEM and Retail Licenses:

Once you have selected Windows 10 select Confirm:

Next you will need to select the Language:


  • English International = English (UK)
  • English = English (US)

Once you have made your selection, select Confirm:

You will be presented a 64 Bit and a 32 Bit Download Link. When you highlight these download links you will see the direct download links to Microsoft's servers and a time limited download token:

On the download page, there will be an option to verify your Download. Clicking this will display the SHA256 checksum for each ISO:

Checking Installation ISO Checksums

To check the Checksum we will use the Terminal Go to Launchpad and then select Other:

Then select the Terminal:

Type in:

cd Downloads

Then type in:

shasum -a 256 YOURISOFILENAME.iso

I recommend using copying your ISO file name and pasting opposed to trying to type it out. Once done press [↵].

Select OK:

The ISO Checksum should match Microsoft's website. If it does not retry the download as your ISO is corrupt:

Creating a Windows 10 UEFI Bootable USB

All systems manufactured in 2012 or later have a UEFI BIOS with Secure Boot. Windows 10 installation media should be setup to accommodate these technologies.

Only 64 Bit Operating Systems are supported with a UEFI Boot.

A GPT partition scheme allows more than 4 partitions on a SSD/HDD which means there are multiple recovery partitions created during the Windows install making the Windows 10 Boot more robust. A MBR partition scheme on the other hand only had one boot partition which could get easily corrupted rendering the Windows 10 OS Unbootable.

Secure Boot prevents malicious code from Booting up before Windows 10, allowing only signed code to Boot. This allows windows 10 and its inbuilt security to Boot before ransomware. Older Windows versions such as Windows XP and Windows 7 were commonly crippled by ransomware as they did not use Secure Boot.

Checking your Install.wim File Size

A Windows 10 UEFI Bootable USB needs to use the GPT Partition Scheme with a FAT32 Partition. The FAT32 file system unfortunately has an upper limit of 4.0 GB and there is usually an install.wim file on the direct download links ISO which exceeds 4.0 GB (this depends on the Windows 10 Version and Language). As a result most Linux Bootable USB utilities will either truncate the install.wim giving incomplete installation media or format the partition as NTFS meaning the Bootable USB won't pass Secure Boot.

Double click the ISO file to open it in Finder.

Go to the sources folder:

Look for the install.wim and copy it to the Downloads folder:

Move your mouse to the top of the Window, select File and select Get Info. If the file size exceeds 4.0 GB (4,294,967,296 Bytes) then it exceeds the upper limit for the FAT32 file format and needs to be split into 2 install.swm files. We will copy it to the downloads folder and split it.

If it does not exceed this limit you shouldn't copy the install.wim over to the Downloads folder or attempt to split it.

Software Install

On a Mac system we need to install a utility called wimlib which we can use to split the install.wim file into two smaller install.swm files. To do this we first need to install brew (which allows for commands similar to apt on Linux). Open up the terminal and type in:

/bin/bash -c "$(curl -fsSL"

Then press [↵]. Input your password when prompted to authorise the install:

Select [↵] to continue:

Brew will install:

Once Brew has installed, use it to install wimlib. Type in:

brew install wimlib

Then press [↵].

wimlib will now be installed:

Splitting the Install.wim File into < 4.0 GB Install.swm Files

Now type in:

wimlib-imagex split Downloads/install.wim Downloads/install.swm 4000

Then press [↵].

Wait for wimlib to finish splitting the install.wim file into the two install.swm files. You will now have two install.swm files.

Formatting a USB Flash Drive using DiskUtil

We now need to create a blank FAT32 formatted USB Flash Drive. Unfortunately if you use the GUI to make a FAT32 formatted USB. The Windows 10 Install will hang at copying files giving the error message. This means the USB flash drive is not properly FAT32 formatted:

Windows could not prepare the computer to boot into the next phase of installation

We can fortunately use the terminal to create a FAT32 formatted USB Flash Drive correctly. Insert a USB Flash Drive and open up a terminal and type in:

diskutil list

Press [↵] to continue:

Look for the number of your disk, in most cases it will be disk2 (it should be external and the size as expected):

Type in the following:

diskutil eraseDisk MS-DOS WIN_2004 MBR /dev/disk2

Although this line mentions MBR, Windows 10 will be installed using the GUID Partition Table (GPT).

Press [↵] to continue.

You should now have a blank formatted FAT32 Bootable USB:

Copying Windows Setup Files

In this stage we are essentially manually copying all the setup files from the ISO to the Bootable USB. If the install.wim exceeds 4.0 GB, we will copy everything across except this file and in its place use the 2 install.swm files.

Go to the mounted Windows 10 ISO. Copy all the folders to the USB except for the sources folder.

On the USB create a new folder:

Name it sources:

Go to the sources folder on the ISO and the sources folder on the USB. Copy all the contents in the sources folder on the ISO except for the install.wim to the sources folder on the USB:

Instead of the install.wim, copy the two install.swm files:

Once the files have copied over you should now have a Windows 10 Bootable USB that passes Secure Boot.

Creating a Windows 10 Legacy Bootable USB (Unsupported)

Unfortunately MAC OS has limited support for the NTFS file format used in a Legacy USB.

PCs manufactured before 2010 have a Legacy Only BIOS and do not support a UEFI Boot. To install Windows 10 on these PCs you need to create a Legacy Bootable USB. A Legacy USB must be used for a Windows 10 32 Bit Install.

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.