If you mark the partition active, it will still boot on UEFI pcs i.e. Step 7 is the ONLY difference beween a UEFI and legacy bios installer. Optional (for legacy bios), make fat32 partition active using diskpart commands. Wipe all partitions on usb drive from disk managementĬopy all files from iso EXCEPT install.wim in sources folder to fat32 partition So, I decided to create a bootable usb drive without using Rufus as follows which I know will work with install.wim over 4 GB as follows I tried this and indeed this was the case. Worse still, you have to disable secure boot to boot from the UEFI version. It still creates an NTFS based legacy bios installer needed if install.wim is over 4GB which will not boot on most UEFI pcs which require a fat32 partition. I then downloaded a Windows 8.1 iso where the install.wim file was less than 4GB.

I suspected the reason was the install.wim file is over 4 GB and cannot be written to a fat32 drive. So you can only create an iso for legacy bios or for UEFI but not both. The first thing that surprised me was the option to create a bootable iso suitable for UEFI and Bios was not there any more. So I decided to do some testing as I have not used it for a while. So many recommend using Rufus which can produce isos for either a UEFI pc or a legacy bios PC.

However, it is not suitable for custom isos, or for earlier versions e.g. The created iso will boot on UEFI or legacy bios. The media creation tool is the easiest way if installing the latest standard 2004 release version.

There are a number of ways i.e use the media creation tool, or download iso and use rufus. I do not take credit for the method - see This mini guide shows how to create a universal usb windows 10 installer that will work on legacy bios or UEFI (even with secure boot enabled).

How to turn off universal usb installer