Boot to Mounted Drive?


New Member
Brief background:
Just downloaded EasyBCD, in process of getting 2nd Laptop for boot experiments but bit new to Boot Options world. Only things actually done in past is create Win10 install USB with ISO and Media tool (used Rufus once also) and created a 3rd party Image backup Emergency Boot USBs with Rufus.
If understand correctly one can create a bootable image (with various softwares) onto physical disk device (HD Partition, DVD, USB etc) and then in bios or UEFI set aforesaid to boot on next start. I understand the term bootable requires a bootstrap and bootloader and sometimes of a specific (first) record format (i.e. UEFI wants FAT32)
Also apparently one can also native boot (MS Windows Specific) a VHD file.

But is it possible (without copying it first to a physical primary partition, HD, USB etc) to Mount a bootable IMG OR ISO file and then set the system to boot from this file?
In other words I'm wondering how Bios or UEFI will (on boot) even knows about mounted files?


New Member
I think I found a good part of my own answer. Apparently (from watching YouTube Videos) one can add an unmounted bootable ISO or IMG File to the Boot Entry via EasyBCD and it then becomes part of the 2nd stage boot loader choices on boot process. It does not say anything about the file needing mounted or even being on the 1st sector of a bootable partition, just the file itself added to the Boot Entry list.

Additionally nothing is said whether the boot loader at any time mounts the file, only that the boot loader can choose the file (image) itself to give control of the boot process. But in any case this somewhat separates it from the initial boot of the Bios (at Ram ffff0) as far as being aware of "where or what" the final OS image is booted from.

Bios Ram code reads the 1st boot sector written prior to the normal boot drive (or whatever device set prior in Bios or UEFI). And from that code it jumps to a boot loader (be it Grub, Bootmgr, etc) and it deals with the entries given it prior. (I'm guessing these are recorded in the boot.ini for Windows).

So still kinda gray on whether a file image mounted or unmounted is academic or mute. Bios (or UEFI) does first look to a locatable device with a bootable image (USB, CD, another Partition, etc), and from that code it jmps to another loader. Other things can happen after Bios turns control over the 2nd stage boot loader before the final process is done.
Looking forward to getting my second sacrificial Laptop to experiment a bit.