Bdtyktl

Starting from a Windows 10 ISO image file with >4GiB install.wim (including current Win10_1809Oct_language_x64.iso of like 4.8GiB built 2018/10/30), how can I make a USB drive that is bootable including on a non-UEFI machine?

MediaCreationTool1809.exe works, but it downloads everything, and modifies at least 3 files: install.esd replacing install.wim, boot.wim, and ws.dat. These changes remove some editions of Windows (e.g. Pro Education and Pro for workstations, and their N variations), and make it impossible to check integrity of the modified files against a fixed hash.

With the help of @AtomiX84's comment I came up with this solution that has worked for me, making a USB drive bootable both on a UEFI and non-UEFI machine. Basically

• We need a FAT32 boot partition in order to be bootable under UEFI.


• The large intall.wim can't be on a FAT32 partition; we'll make a second ExFAT partition.


• We then need to invoke BOOTSECT in order to be bootable on a non-UEFI machine.

Under a working Windows 10:

• Connect an 8GB USB drive (or larger up to 32 GB)


• Launch DISKPART (press the Windows key, type DISKPART, agree to all) and in the window that opens (lowercase letters optional)
  
  
  
  
  • LISt DISk
  
  
  • 
    SELect DISk N (replace N with appropriate number)
  
  
  • !! Triple-check the disk number !!
  
  
  • 
    CLEan (occasional access error can typically be ignored)
  
  
  • CONv MBR
  
  
  • 
    CREate PARtition PRImary OFFSET=32 SIZE=512 (that's in MiB; with current Windows 10 we need at least about 450, and at most about what LISt DISk has shown for the drive minus 4900)
  
  
  • FORmat FS=FAT32 QUICK LABEL=WIN10_FAT32
  
  
  • 
    ASSign LETTER=X (assuming this drive letter is unassigned)
  
  
  • ACTive
  
  
  • CREate PARtition PRImary
  
  
  • FORmat FS=EXFAT QUICK LABEL=WIN10_EXFAT
  
  
  • 
    ASSign LETTER=Y (assuming this drive letter is unassigned)
  
  
  • EXIt
  
  
  
  


• Exectute CMD as administrator, and in that window
  
  
  
  
  • 
    BOOTSECT /NT60 X: /MBR (where X is the drive letter for the WIN10_FAT32 mounted partition)
  
  
  • 
    MD X:sources (where X is as above)
  
  
  • EXIT
  
  
  
  


• If 7-zip is available (recommended as it keeps expanded folder dates) open the ISO file with 7-zip
  
  
  
  
  • Select all files and folders (Ctrl-A), and extract/copy to.. (F5 - do not drag) towards the WIN10_EXFAT mounted volume (Y:)
  
  
  • Select all files and folders except the sources folder (Ctrl-A, shift-click), and extract/copy to.. (F5 - do not drag) towards the WIN10_FAT32 mounted volume (X:)
  
  
  • Enter the ISO's sources folder, select boot.wim, and extract/copy to.. (F5 - do not drag) towards the sources folder of the WIN10_FAT32 mounted volume (X:sources)
  
  
  • Close 7-zip's window
  
  
  
  


• Or, lacking 7-zip, mount the ISO (e.g. Open with.. Windows Explorer) and
  
  
  
  
  • Copy the mounted volume's whole content towards the WIN10_EXFAT mounted volume (Y:)
  
  
  • Copy the mounted volume's whole content except the sources folder towards the WIN10_FAT32 mounted volume (X:)
  
  
  • Copy boot.wim of the mounted volume's sources folder towards the sources folder of the WIN10_FAT32 mounted volume (X:sources)
  
  
  • Eject the volume for the mounted ISO
  
  
  
  


• Eject the USB drive (both volumes)