Create Windows 10/11 installation media without additional software

When you try to make a bootable USB flash drive to install Windows 10/11 from an .iso image, you seem to run into a predicament:

• The install.wim file exceeds the maximum file size supported by the FAT32 file system, so you need NTFS.
• Some EFI systems cannot boot from NTFS-formatted flash drives, so you need FAT32.

Luckily, you can use FAT32 and split the install.wim file with tools already built into Windows, and the resulting flash drive will be able to launch Windows Setup on any EFI system:

1. Download a Windows 10 or Windows 11 .iso file from Microsoft, such as Win11_25H2_English_x64_v2.iso.
2. Verify the integrity of the .iso file in PowerShell:

   Get-FileHash -LiteralPath "…\Win11_25H2_English_x64_v2.iso";

3. Remove the Mark of the Web of the .iso file. You can do this in File Explorer, or run this PowerShell command:

   Unblock-File -LiteralPath "…\Win11_25H2_English_x64_v2.iso";

4. Mount the .iso image in File Explorer. This tutorial assumes that the .iso image is mounted to the D:\ drive.
5. Plug in a USB flash drive with a capacity sufficient to store the contents of the .iso image plus your custom files, such as those in the $OEM$ or $WinPEDriver$ folders.

   Windows Setup tends to be somewhat picky with USB flash drives and might produce strange or misleading error messages when a drive is unreliable.

   I recommend using USB 2.0 flash drives for Windows Setup as these seem to be less erratic, and their lower speed is of no real consequence here.

6. Using diskpart.exe or diskmgmt.msc, wipe that drive, create a single partition and format it with the FAT32 file system. This tutorial assumes that the flash drive is assigned the E:\ drive letter.
7. Launch a PowerShell session with administrative privileges:
   1. Copy the contents of the .iso image to the flash drive, but omit the large install.wim file:

      Copy-Item -Path 'D:\*' -Destination 'E:\' -Recurse -Force -Exclude 'install.wim';

   2. Copy the large install.wim file to the flash drive in chunks of 2 GiB:

      Dism.exe /Split-Image /ImageFile:"D:\sources\install.wim" /SWMFile:"E:\sources\install.swm" /FileSize:2048;

8. Unmount the .iso image.