Windows Bootable USB and UEFI Boot Mode with Secure Boot

Question

Microsoft offer Windows Installation Media as ISO files using Direct Download Links. How do I make a UEFI Bootable USB that passes Secure Boot on a Dell system from the ISO?

Note this applies to only the ISO files from Microsoft Windows 10, Windows 11, Windows Insider Preview Direct Download Links and not ISO files created via the Media Creation Tools.

Windows Insider Program using ISOs

Answer

Many Dell systems expect Bootable Media to have a FAT32 Boot Partition. One of the limitations in the FAT32 File System is the upper file size of 4.0 GB. Recent Microsoft installation media from direct download links include an install.wim that exceeds 4.0 GB and therefore if a solo FAT32 Partition is used, the install.wim is truncated and the installation media is therefore corrupted.

To get around this we can create a multi-partition USB with a FAT32 BOOT Partition and NTFS INSTALL Partition.

Setting up a GPT Partition Table on the USB

First we will use Rufus to create a non-Bootable USB with a GPT Partition Table. 

Rufus 

Select your USB under the Device drop down. Under Boot Selection, select Non Bootable. Under Partition Scheme select GPT and under Target System select BIOS or UEFI. Use USB as the Volume Label and the FAT32 File System. Select Start and then accept the warnings in order to proceed.

 

Delete the FAT32 Partition on the USB

Insert your >16 GB USB Flash Drive and right click the Start Button and select Disk Management. Delete the FAT32 Partition on your USB Flash Drive. It should now say unallocated space.

Create a FAT32 BOOT Partition

Right click the unallocated space and select New Simple Volume... Select Next.

• Change the Simple Volume Size in MB to be 1024.
• Assign the following drive letter e.g. to I:\
• Then Format the File System with the FAT32
• Call the Volume Label: BOOT.

Select Next and Finish.

If the USB partition does not say FAT32 and instead says RAW. Right click it and select Format once again selecting FAT32 and ensuring the Volume Label is BOOT.

Create a NTFS INSTALL Partition

Right click the unallocated space and select New Simple Volume... Select Next.

• Use the default value for the Simple Volume Size in MB (which will span the rest of the USB Flash Drive).
• Assign the following drive letter e.g. to J:\
• Then Format the File System with the NTFS.
• Call the Volume Label: INSTALL.

Select Next and Finish.

Copy BOOT Partition Files

Copy all the files/folders from the Windows Installation ISO to the BOOT Partition except for the sources folder. 

In its place create your own sources folder. In this sources folder copy the boot.wim file from the original sources folder of the ISO.

 

Copy INSTALL Partition Files

Copy all the files/folders from the Windows Installation ISO to the INSTALL Partition. Note it may take several minutes for the large files to fully copy over to your USB.

 

Your Bootable USB is now ready.

Booting from your USB

Power off your Dell Computer and insert your Bootable USB. Power it up and press [F12] to access the BIOS Boot Menu. The Boot Mode should be set to UEFI and Secure Boot should be ON. Select your USB Flash Drive. This will Boot using the FAT32 BOOT Partition which will use the files on the NTFS INSTALL Partition during the Windows Setup.