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Windows 8.1 + Windows 10 UEFI ISO boot


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#26 Wonko the Sane

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Posted 24 December 2015 - 11:42 AM

I work as a PC tech and i have clean installed Windows 8.1 x64 /Windows 10 x64 to PC/laptops from all major manufacturer's and custom built systems. I can safely say that all UEFI firmware will support and boot from MBR formatted USB flash drives (FAT32).

That would be of course "a large number of" major manufacturer's and custom built systems. ;)

Black swans are rare, but they do exist.

https://en.wikipedia...ack_swan_theory

 

However there are some buggy firmware which will only boot to UEFI mode if there is a valid UEFI bootloader is present on the USB stick. One particular example is newer Acer laptops. They will only boot to UEFI mode if "efi" folder is present on the root of USB stick (with EFI bootloader inside it) - even though boot mode is set to legacy only in BIOS setup. Only way to install either Windows 8.1/Windows 10 in legacy mode on that system is to delete or rename "efi" folder on the root of USB stick. 

You mean "will only boot in non-UEFI mode if a valid UEFI bootloader is not present", I believe or - in other words - even if the boot mode is set to "legacy" in BIOS, if there is an EFI bootloader on the stick, than UEFI mode will prevail? :unsure:

I mean, if there is no EFI bootloader the thingy won't boot to UEFI (of course).

 

:duff:

Wonko



#27 Agent47

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Posted 24 December 2015 - 01:05 PM

 

 

You mean "will only boot in non-UEFI mode if a valid UEFI bootloader is not present", I believe or - in other words - even if the boot mode is set to "legacy" in BIOS, if there is an EFI bootloader on the stick, than UEFI mode will prevail?  :unsure:

 

Yes, that's exactly what i meant. The F12 boot menu also behaves like the same - it will only list UEFI boot entries if there is an EFI boot loader is present on the stick.

 

 

 Could you list the models that won't CSM boot if a EFI boot file is present please?

P.S. You can UEFI-boot and CSM-boot on these 'bad' systems if using Easy2Boot (sort of!).

 

I don't remember an exact model number but i believe most of the Acer E1 series laptops has this issue. I will try to reproduce the issue as soon as i got some Acer laptops and post back some full model numbers.

 

 

My rufus formatted USB stick ( removable type ) does not boot on my MS Surface Pro.

 

 

 

In that case i guess i was wrong. I never had a chance to play with "Surface Pro" . 



#28 steve6375

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Posted 25 December 2015 - 09:10 AM

I think that a bootable FAT32 USB stick containing the correct EFI boot files should boot on a Surface Pro (same as MS tool makes).

AFAIK the Surface Pro is UEFI only (no CSM mode?).



#29 paraglider

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Posted 25 December 2015 - 09:27 AM

Yes - no CSM. You can disable secure boot though. MS does claim that a fat32 usb drive should work.



#30 Agent47

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Posted 04 February 2016 - 07:00 AM

 

ould you list the models that won't CSM boot if a EFI boot file is present please?

P.S. You can UEFI-boot and CSM-boot on these 'bad' systems if using Easy2Boot (sort of!).

 

 

Here is the full model number of an Acer laptop which has the EFI bug - Aspire E1-571. Most probably other E1 models might be also affected ( may be E3 and E5 series too). 

 

Steve, can you please explain how Easy2Boot can be used to CSM boot on these type of firmwares ?. What exactly Easy2boot  will do on these  kind of scenarios ?.



#31 steve6375

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Posted 04 February 2016 - 09:10 AM

Thanks. 

Does it have firmware version 2.21?

Just to double-check - you have tried all BIOS Setup options, etc. to try to get CSM boot working?

Does CSM boot work if you delete the \EFI\boot\bootx64.efi file?

Does CSM boot work if you delete the \EFI\boot folder?

Does CSM work if you delete the \EFI folder?

 

re. Easy2Boot. Easy2Boot does not have a \EFI folder, when it switches partitions to CSM mode, it does have both CSM boot files and EFI boot files and so can only CSM boot on the E1-571 system, but you can run the Windows app  SWITCH_E2B.exe to restore the original E2B partitions (that is why I said 'sort of')!



#32 Agent47

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Posted 06 February 2016 - 10:43 AM

Hi

 

Sorry for the late reply. Unfortunately the customer was in a hurry (owner of the lap) so i was unable to complete all the tests. However i can guarantee that i have tried all the possible settings on BIOS setup. Next time i will try all those scenarios and report back. I also have a plan to experiment with "rEFInd" which has an option to boot from a legacy device if the BIOS has CSM support enabled.






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