Howto Make Drive Bootable
It is forever problem to make disc bootable and adapt to media size simultaneously. It is because each time MBR must be adapted, which is sort of black magic. At least less documented.
One of the useful utilities is ms-sys. (I’ve probably copied following from somewhere)
Needed (for Windows):
- Modified SETUPLDR.BIN
- Special stuff in the bootsector of the partition (use ms-sys).
- Modified copy of txtsetup.sif copied to the root level
- NTDETECT.COM copied to root level
With UEFI it’s simpler - just a magic directory and UEFI is able to detect it and run.
I don’t know current state since written partitions can resize on the first boot, live systems can save settings and other stuff and I don’t know how they do it. Yet.
You can use Unetbootin, Rufus, Balena Etcher and other. But only Rufus (Windows only :-/) works reliably well. But it’s useful to know low level utilities like ms-sys or syslinux or what is actually happening.