Question ISO images bootable only in Legacy BIOS OR (!) UEFI ? Decision at ISO creation time or at storage on USB flash drive?

pstein

Honorable
Oct 2, 2013
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As you known there are many sofwtare tools available which offer not only a setup.exe but an ISO to download.

This ISO can either be burned on a CD/DVD or put onto an USB Flash drive.

I am NOT talking about Win10 ISO images but other software like (examples):
The problem is NOW that when I store one of these ISOs onto an USB Flash drive (with the famous, well known Rufus v3.5 tool) then
they are oftentimes bootable only on Legacy BIOS computers.

On other UEFI-based computer (with disabled Secure Boot) the same USB flash drives are not even recognized in Boot menu.

Why?

Are ISO images only created for Legacy BIOS OR(!) UEFI ?
Or can they be created to work with both BIOS types?

How do I find out for a given ISO if its working with (only) Legacy BIOS or UEFI (without trying it out)?
Is there a tool which shows it or a file inside the ISO which indicates it?

At which point resp. step is the decision made for which BIOS type it is working?
Is it done at ISO creation time or is it done at storage time on USB flahs drive (=inside e.g. Rufus)?

Thank you for commenting
Peter
 

Traditore

Honorable
Nov 5, 2013
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52
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Isn't enabling CSM support in BIOS allows non-UEFI GRUB to boot? Or is it that you specifically need GRUB in UEFI as your OS?

Anyway.

The ISO image on the latest GParted doesn't work properly for UEFI boot by default. I've outlined how to fix it, but it requires a UEFI Clonezilla image.
  • get and run Unetbootin as an admin and create the latest version of GParted image on a flash drive per the norm
  • Copy the \boot\ directory from a clonezilla ISO/configured flash drive to the root of the newly created GParted flash drive
  • Copy the following files found in \EFI\boot\ (ignore the x86_64-efi folder) to the same directory on the newly created GParted flsh drive: bootia32.efi bootx64.efi grubx64.efi unicode.pf2
If you get a prompt from UNbootin asking to overwrite the syslinux\menu.c32 file, click No. Or if you get an error when booting from the flash drive regarding the syslinux\menu.c32 file, overwrite that from a clonezilla ISO too.

Are ISO images only created for Legacy BIOS OR(!) UEFI ?
Or can they be created to work with both BIOS types?
They need specific files present in the image to enable UEFI boot. So, it's the creator of the image who makes it bootable either way.

How do I find out for a given ISO if its working with (only) Legacy BIOS or UEFI (without trying it out)?
Is there a tool which shows it or a file inside the ISO which indicates it?
I always create any bootable USB with Rufus. After you pick an image you want to burn, it shows whether UEFI or/and MBR avaiable.
Also, files mentioned above in my answer are the files that indicate UEFI boot compatibility.

At which point resp. step is the decision made for which BIOS type it is working?
Is it done at ISO creation time or is it done at storage time on USB flahs drive (=inside e.g. Rufus)?
The image has to have certain files to enable UEFI boot. Any software simply recognizes the possibility of UEFI. CD/DVD are always made UEFI+MBR bootable IF image has UEFI files, while with flashdrives you can make MBR only bootdrive even if UEFI is possible, the software gives an option.
 
Last edited:

popatim

Titan
Moderator
UEFI or Legacy is dependent on the OS you install to the flash drive.
Rufus detects what you are installing and create the appropriate Flashdrive type.

So basically you picked the wrong Iso's. Clonezille and Gparted bith have AMD64 versions that support UEFI boot.
I'm not familiar enough with Minitool to know if it supports UEFi or not.
 

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