[MinnowBoard] What must a Linux .ISO contain for UEFI booting?

Jim Elliott james_m_elliott at yahoo.com
Fri Jul 15 21:30:57 UTC 2016

Minnowboard Turbot bought June 2016UEFI interactive Shell v2.1EDK IIUEFI v2.40
After downloading a Linux distribution .ISO, with Nemo, I right click on the .ISO and select "Make bootable USB stick" and select a microSD held in a gizmo that lets me plug it into a USB port.
Can anyone provide a link to an explanation of how a microSD must be formatted (partitioned, initialized, or otherwise written) to boot UEFI?  I believe that often, a file named (idential to, something like?) bootx64.efi in /EFI/BOOT is needed.  For example Linux Mint Mate boots from microSD when I select "EFI Misc Device" in the UEFI GUI.  It has both /EFI/BOOT BOOTx64.EFI and grubx64.efi
By contrast, Portius has bootx64.efi in /EFI/BOOT but it won't boot.
Fatdog64-702.iso boots without any EFI or BOOT directory.  Its website says it is "dual-isohybrid ISO".
Am I unknowingly booting (always?  sometimes?) in some sort of legacy mode?
Going back to the UEFI shell.  One thing that seems essential is the presence of fs0: in the "Mapping table" but I don't understand what makes that present or not.
Other strangeness I cannot explain:After writing with Nemo and "Make bootable USB stick", I examine /dev/sdb with the "Disks" utility.  It shows one (what, Volume?  Partition?) labeled "Linux Mint MATE 18 64-bit" "Contents ISO 9660" taking up the entire 15GB microSD.But after I move the microSD to the Turbot, boot, take it back out and examine it again with Disks on my desktop PC, there are three Volumes, the previous Linux Mint 18 "Partition 1" but shrunk to 1.8 GB, "Linux Mint Partition 2" "2.4 MB FAT", and 14GB "Free Space".  What happened?  Did Disks show the microSD incorrectly just after I wrote the .ISO to it?  Did the process of booting Mint reconfigure the microSD?(I'll try to attach two screen shots)
I have better luck writing to a microSD than a USB "stick" but cannot explain why Linux .ISOs on these two devices would behave differently when attempting to boot.  Worse, writing Fatdog to a stick renders it nearly impervious to formatting and restoration to its customary use to hold files (gparted complains bitterly about the presence of a GPT, "Disks" says " Error synchronizing after initial wipe: Timed out waiting for object (udisks-error-quark, 0)").  My only remedy was to ask Disks to edit the partition to HPFS/NTFS (0x07).
For some Linux distributions asking Nemo by right clicking the .ISO to "extract here"  yields "Error creating directory: Permission denied". 
Thank you for any suggestions and clarification.Jim
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