Is your UEFI able to boot iso in partition?

[teika]

*EDIT* (2024-07-29): Posted the same question at Arch forum.

Suppose you have the iso image of a bootable medium in a partition, copied with dd:
  $ dd if=<iso image> of=/dev/disk/by-foo/bar bs=1M

I found at least in two PCs the UEFI boot option menu shows this iso as a choice, and in fact it is possible to boot it. (One does not even has an optical drive.) No bootloader is necessary.

Question: Can your PC boot one? Let us limit to the Gentoo Live media.

In fact I prepared two isos, the minimal (amd64) CD and the LiveGUI image, put in an external USB drive. (So you need *two* partitions in this case.) In one PC, they are shown as:
 USB Hard Drive (UEFI) - Generic External
 USB Hard Drive (UEFI) - Generic External
In the other device, the menu reads:
 DVD1-1 (<hdd id>)
 DVD2-1 (<hdd id>)
The order did not necessarily coincide with the partition order, so if you have two, there's no guess which is which.

If this is the common case, I'll tell the Handbook maintainers about this. At least, it is worth trying rather than dedicating an entire drive for installation.

In my PC without the optical drive, its dmidecode says boot from cd is supported.

# Did you know that many PCs still support boot from a floppy.? ;-)
# BTW Today even "minimal" cd is 500MiB big. Your old auntie will be surprised! ;uu

According to LLM AIs, such boot is unlikely to be possible. So perhaps this is not part of the UEFI specification, and this is little known. Maybe I'll ask this again at stackexchange/reddit.

Personally I always want to have a live medium at hand for a rescue purpose, and I have been struggling for years preparing one using grub. It's really cumbersome. To my both joy and disappointment, such effort was a waste, at least for me; dd and you're done.

EDIT:
@AndrewAmmerlaan: Thanks. Most people do not know much about such thing!
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