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How to create an EFI bootable Windows installer USB stick w/o Rufus ?
Dear forum readers,
I downloaded the official 21H1 ISO from Microsoft. Unfortunately however, MS doesn't make hybrid ISO images, hence it won't boot when written to a USB stick. Some BIOSes provide CD/DVD emulation, but it generally doesn't work well, and fail at some point.
That's why I'm trying to change a few things to get the installer working on a USB stick. I know there are helper programs that will do the job such as Rufus or MCT, but there are reasons to try without such programs :
- Being on a non-Windows OS
- MCT doesn't produce installation medium in a reproducible hence verifiable way
- Remaining autonomous as much as possible, not relying on helper programs
I've read that things were as easy as formatting the stick in DOS/MBR format, creating one FAT32 partition and copying the contents of the ISO to the root of the partition. In case some files are too big (> 4096 MiB), it's most likely the one namedinstall.wim
, either convert it in ESD format (install.esd
) or split the file in smaller SWM chunks (install.swm
,install2.swm
).
I did that, it didn't work. I tried with formatting in GPT format instead, with the partition type being either EFI or Microsoft Basic Data, no more luck.
I can see it starts booting, with some serious access to the USB stick, but it always ends up either freezing or rebooting. What am I missing ?