ISO images bootable only in Legacy BIOS OR (!) UEFI ? Decision at creat.time?

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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):
– Gparted https://gparted.org/livecd.php
– Partition Wizard https://www.partitionwizard.com/partition-wizard-bootable-cd.html
– Clonezilla https://www.clonezilla.org/downloads.php

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

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Terms can be confusing.  Storing of an .iso file on an HDD, CD/DVD or Flash drive does not make it bootable.  Downloading an .iso file then using File Explorer or a third-party program such as Roxio can create/burn the bootable CD or DVD disc used to install from.  The .iso file is used to create an exact duplicate of the original disc.

If Windows is running I do the Upgrade from within File Explorer, if the HDD is clean I boot to the disc or thumb drive and just let Windows do its thing, create as needed.

Before you wonder "Am I doing things right," ask "Am I doing the right things?"

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[Microfix]

I know of Minitool Partition Wizard as I have v9 on a Flash drive and find it the quickest way to do anything with a HDD or SSD. That particular ISO is based on linux (corelinux IIRC) to access the HDD/SSD subsystem with a GUI during flash drive booting (point and click easy to use interface)

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

It may depend on the hardware technology/ bios per device or what OS and AV is on the device protecting things…It may also depend on what settings were chosen when burning the chosen program ISO to the flash drive within the Rufus utility.
It may be worthwhile checking out the rufus settings for your requirements via search online.

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• This reply was modified 5 years, 11 months ago by Microfix.
• This reply was modified 5 years, 11 months ago by Microfix.

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MBR/legacy requires specific files in a specific area of the disk, not normally available to users. UEFI only requires a boot file in a specific directory on a standard formatted disk.
You can have both on a USB / HDD / SSD but the machine you boot from may or not be capable of using both.
This post may help.

cheers, Paul

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Oh and a “bootable ISO” might also be for something completely different instead of a PC. All it really says that the ISO, when written directly to optical disk of the appropriate type, would be bootable in whatever kind of device it’s for.

In contrast if it’s .IMG it probably goes on a different kind of media, most likely USB flash these days but in the past might have been floppies or even tape…

Some really work only in a specific hardware model. Any number of weird devices like that, the farther you go from a standard PC… I mean, some devices even if they run Windows have to be initially installed off special boot media. (And with some of these, reinstall media was an expensive extra-cost option. Then the fancy thin-client customized Windows 8 got autoupdated to 10 and failed to work, and… well. At least for some of those devices I now know where to find the reinstall media.)

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[doriel]

Hello,
there is hidden tweak in Rufus, if you press ALT-E, you enable “dual boot” mode. This option is not visible, but it works. Maybe this should help.

I mean you dont need to decide, it should work both ways and you even do not destroy your boot record tables like I did when I tried very hard

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• This reply was modified 5 years, 11 months ago by doriel.

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Ascaris

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[EP]

although there may be some issues when using Alt+E to enable dual uefi/bios boot mode documented by the creator of Rufus:

https://github.com/pbatard/rufus/issues/708

https://github.com/pbatard/rufus/issues/838

it may work for some but others it may not

Rufus FAQ on dual uefi/bios mode:
https://github.com/pbatard/rufus/wiki/FAQ#Why_doesnt_Rufus_create_a_Windows_installation_USB_that_can_be_booted_in_dual_BIOSUEFI_mode

• This reply was modified 5 years, 11 months ago by EP.

1 user thanked author for this post.

Ascaris

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