Why won't Ventoy boot a Microsoft Windows 10 ISO file?

[Renatus]

You said 'so it boots from the MBR, doesn't need EFI partition for booting.'

If you make a fresh Ventoy USB drive, then partition 1 is completely empty - but you can Legacy boot from the USB drive to the Ventoy menu (which then reboots because the partition 1 is empty). The Legacy boot files are on Partition 2. It DOES need the EFI partition for Legacy booting.

Please can you add screenshots of standard Ventoy USB drive with the two Windows files in the Ventoy menu.
Then show screenshot of UEFI-booting 'good' ISO and screenshot of booting 'bad' ISO.

Also, try formatting first partition as NTFS.

I can boot the ISO OK (partition 1 = NTFS, older Ventoy than you).

Another explanation is that NUC is causing an issue. Can you boot on different systems as a test?

Hi Steve, sorry but you are wrong in relation the need to have a EFI partition to boot, you only need the MBR to boot in legacy mode, you can check here https://ventoy.net/en/doc_disk_layout.html in the MBR section.
In old or legacy systems, EFI partition never existed and in fact is not needed, only when EFI was introduced by Intel, a new partition EFI, was needed for the system to boot, Ventoy allows both methods to work.
I tried as you suggested booting on another system, this time on a ASUS Deskmini X300, this system only allows UEFI booting, not legacy booting, and in fact it works with the same ISO that doesn't work in the NUC when I use UEFI booting, in both cases as expected the systems boot from the second partition.
So, it seems the NUC is the culprit, and that's odd, because the NUC is an Intel PC and it was Intel that invented the EFI specification.

[Steve2926]

If you make a fresh Ventoy USb drive, the first partition is completely empty. So how can it legacy boot? You can even reformat it and it will still legacy boot.
If you delete ALL the files on the second partition, you will find it will not legacy boot.
The Ventoy documentation clearly states that partition 2 'For EFI boot and hold Ventoy files'

[FroggieTheGremlin]

In an MBR-Legacy BOOT configuration, the MBR (or EMBR if used) directs the System as to where to go for BOOTing. In a normal System MBR configuration it is directed to the ACTIVE partition for BOOTing... but it may be directed anywhere by the MBR BOOT code, including an EFI partition located anywhere on that disk.

Steve is correct, the BOOT code used for MBR Systems is actually located in Partition #2, the EFI partition, which is fine... it can be anywhere the MBR BOOT code directs it to be. Longpanda has chosen to use the same partition for BOOTing regardless of whether the System is MBR-Legacy or UEFI-GPT configured... there's no problem with this that I know of.

[Renatus]

In an MBR-Legacy BOOT configuration, the MBR (or EMBR if used) directs the System as to where to go for BOOTing.  In a normal System MBR configuration it is directed to the ACTIVE partition for BOOTing... but it may be directed anywhere by the MBR BOOT code, including an EFI partition located anywhere on that disk.

Steve is correct, the BOOT code used for MBR Systems is actually located in Partition #2, the EFI partition, which is fine... it can be anywhere the MBR BOOT code directs it to be.  Longpanda has chosen to use the same partition for BOOTing regardless of whether the System is MBR-Legacy or UEFI-GPT configured... there's no problem with this that I know of.

Yes of course, I know all that, the MBR directs the system to the active partition (normally), what I meant is that you don't need an EFI partition when you do a MBR boot, in the particular case of Ventoy, the "active" partition is the EFI partition, but that's a particular case. I spoke about the general process, and there you don't need a EFI partition, in fact before someone invented EFI, that was how systems (PCs) booted.
When you do a UEFI boot you are looking for .efi file on the EFI partition, on the MBR boot you act differently, although it's not clear in Ventoy's case how it proceeds, I suppose it follows a different method related to grub, for sure it does not depend on the EFI folder because Ventoy (in legacy mode) still works even with no EFI folder.
Anyway, independently of this, newest Windows 10 ISOs, do not work properly in the NUC system with Ventoy, in my last post I said the NUC was the culprit, but I should better say that there is a incompatibility between the NUC booting in UEFI mode and Ventoy when we use a recent Windows 10 ISO, perhaps Ventoy is not working in this scenario, in fact the creator of the tool didn't said it would work with all ISOs.
Regards

[Steve2926]

There indeed may be an incompatibility somewhere. But it could be due to many things.
1. Arrangement of files on Partition 1 and filesystem format, fragmentation of ISO file on USB drive, start position of file, size of ISO
2. Type of filesystem on partition 1 (exFAT or NTFS)
3. Firmware - does same USB drive work on different computers (UEFI64 boot)?
4. ISO - if the new 'bad' ISO fails using a completely different type of computer, a completely different USB drive, both NTFS and exFAT partition 1 (freshly formatted), then it points to a bug in the MS ISO itself (unlikely).

So, I would (after checking for NUC BIOS update and retesting)
1. Test the same Ventoy USB drive and ISO file on different systems
2. Defragment all files on the USB drive and make all files contiguous - re-test on all systems (use Defraggler or WinContig)
3. Reformat partition 1 as NTFS, copy the 'bad' ISO on and test again - test on all systems available
4. repeat 3 but use exFAT
5. Try same ISO using a different USB multiboot solution - e.g. Easy2Boot which also uses grub2, WinSetupFromUSB which uses bootmgr (should work), SARDU, etc.

[Renatus]

There indeed may be an incompatibility somewhere. But it could be due to many things.
1. Arrangement of files on Partition 1 and filesystem format, fragmentation of ISO file on USB drive, start position of file, size of ISO
2. Type of filesystem on partition 1 (exFAT or NTFS)
3. Firmware - does same USB drive work on different computers (UEFI64 boot)?
4. ISO - if the new 'bad' ISO fails using a completely different type of computer, a completely different USB drive, both NTFS and exFAT partition 1 (freshly formatted), then it points to a bug in the MS ISO itself (unlikely).

So, I would (after checking for NUC BIOS update and retesting)
1. Test the same Ventoy USB drive and ISO file on different systems
2. Defragment all files on the USB drive and make all files contiguous - re-test on all systems (use Defraggler or WinContig)
3. Reformat partition 1 as NTFS, copy the 'bad' ISO on and test again - test on all systems available
4. repeat 3 but use exFAT
5. Try same ISO using a different USB multiboot solution - e.g. Easy2Boot which also uses grub2, WinSetupFromUSB which uses bootmgr (should work), SARDU, etc.

I don't believe the problem is related with file system or fragmentation, I tried the same ISO on another system and it works.
It's not a big deal because for instance Rufus is working, I may also try Easy2Boot (thanks for the suggestion).
Perhaps Longpanda is watching this comments and can better understand what could be the cause of incompatibility.

[rkr87]

For anyone else that comes across this thread while trying to figure out this issue, I figured out what it was, at least from my side, though reading through the thread I seem to have been having the exact same issue (older Vs newer ISOs, bios Vs uefi etc).

I resolved the issue by formatting the Ventoy partition as NTFS.

When booting in legacy mode all windows setup ISOs (old and new) seem to work in normal mode.

When booting in UEFI mode, newer ISOs will need WIMBOOT mode to be enabled, older ISOs seem to work in normal mode.

Since applying NTFS and applying above logic I haven't yet found a windows ISO I wasn't able to boot.

[nguyen ha thai trong]

What is your problem in the end?