Solving Windows 10 ISO Size Issue for FAT32: Split or Extract Install.wim

Microsoft ISO files for Windows 10 Volume License and maybe others as well are bigger than 4 GB in total but also contain an install.wim with a size of more than 4 GB. This does not allow creating, for example, a USB stick with a FAT32 file system and would require use of NTFS instead.
If you want to boot under UEFI you might fail, as not all systems can boot from external boot media using NTFS.

1. Extract the needed index/edition from the original install.wim to get a smaller one
2. Split the install.wim file into smaller ones - preserves all editions within the ISO

Extract the needed index/edition from the original install.wim to get a smaller one

Option 1 can be done as follows (DISM commands as available under Windows 10 RS4 - might be adapted to other operating system versions):

1. Extract the required install.wim out of the ISO file or mount the ISO file

2. Open an elevated command prompt to use Microsoft Windows Deployment Image Servicing and Management (DISM) commands

3. Run the following DISM command with the correct path to the install.wim to get the index that represents your needed Windows edition:

   dism /Get-WimInfo /WimFile:"c:\temp\install.wim"

   The output might look like the following:
   
   (Figure 01)

4. Now extract the right index (3 in this case as I want to install Enterprise edition) into a new WIM file using the DISM command:

   dism /Export-Image /SourceImageFile:"c:\temp\install.wim" /SourceIndex: 3 /DestinationImageFile: "c:\temp\install_3.wim"

   This will then look like the following:
   
   (Figure 02)

   It reduced the file size from 4.11 GB to only 3.68 GB which now fits within the file size limitation of FAT32. You now have to rename the created file to install.wim

5. Insert the newly created install.wim into the original ISO file or just copy it onto an already prepared USB stick with all the other needed files from the original ISO

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Split the install.wim file into smaller ones - preserves all editions within the ISO

Option 2 can be easily done as follows:

1. Extract the required install.wim out of the ISO file or mount the ISO file

2. Open an elevated command prompt to use DISM commands

3. Run the following DISM command with the correct path to the install.wim and the wanted file size in MB:

   dism /Split-Image /ImageFile:"c:\temp\install.wim /SWMFile:"c:\temp\install.swm" /FileSize: 4000

4. Now just replace the original install.wim with the created SWM files (install.swm, install2.swm)

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