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I downloaded the Windows 10 version 1909 ISO and created USB installation media on MacOS using UNetbootin.

On the Windows target machine, the installation program started properly. It asked about my location, keyboard and so on. But upon beginning the actual installation, it gave the error:

Windows cannot open the required file D:\Sources\Install.wim.

Make sure all files required for installation are available and restart the installation. Error Code: 0x800700D

Contrary to what the message says, the file exists. What is the problem?

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In older versions of Windows 10, install.wim was smaller than the FAT32 file system 4GB maximum file size. Thus various people created applications and how-to articles that use a USB drive formatted with FAT32.

Then, sometime around 2018, install.wim grew to exceed the FAT32 limit. In Windows 10 version 1909, file install.wim is 4.6GB. Surprise! Even if install.wim is present, it is truncated to 4GB and therefore invalid. Now all those nice applications and instructions that people wrote in the past no longer work.

The NTFS and ExFAT file systems can handle large files--if you are lucky, your BIOS might support NTFS, but the UEFI standard mandates only FAT16 and FAT32.

The solution is to create two partitions. The first is a FAT32 partition containing an NTFS driver. This is used to access the big files on a second NTFS partition.

The Rufus application on Windows automatically creates such a two partition USB installation drive. I used it and it worked. I gave up on MacOS because it cannot write to NTFS without a special driver.

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  • @Ɓaptiste Ɋuinternet, thank you for your edit to my answer. It contained information useful as a separate answer. Please post your own answer and get the reputation you deserve! Mar 30 '20 at 22:42
  • but, the installer is an iso image, how does an iso image from the vendor contain fat32 partition.. ~~then how does the vendor get as far as to distribute obviously corrupt installation media~~ Aug 7 '20 at 22:33
  • nm, i expect this is a unetbootin specific imaging problem Aug 7 '20 at 23:07

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