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I booted from my USB flash drive to install Windows 10 with Fall Creators Update. When booting, I had to change the boot mode to legacy in order to see my USB flash drive in the bootable devices list.

While installing Windows, I deleted all partitions on my drive, and let Windows create what it needs, which currently are a 500 MB "System Reserved" partition and another 476 GB primary partition. I noted that in a past clean install, Windows created 3 partitions, the name of the other which I cannot remember.

Now, I am unable to boot into Windows unless I enable legacy mode, otherwise in UEFI mode it shows 'No boot device found'. This applies to both my Asus X751L running American Megatrends BIOS and my Acer Aspire S5 running InsydeH2O BIOS.

How can I boot in UEFI mode?

George Tian
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2 Answers2

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How can I boot in UEFI mode?

Use the MBR2GPT tool built into Windows 10 1703 (Creators Update) and 1709 (Fall Creators Update). Microsoft has a technical article with a video that might be helpful.

Convert from BIOS to UEFI with MBR2GPT

Once you have converted your installation to GPT, you will have to enable UEFI mode, in order for Windows to actually boot.

Ramhound
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once you have installed in Legacy mode, you cannot revert back to UEFI mode (at least without spending a lot of efforts which is possibly not worth it). because Legacy mode uses MBR records while UEFI mode uses a special partition named EFI (3rd partition) where your UEFI records reside and their corresponding (pointing GUIDs and which folders with bootloaders responsible to load that OS on EFI partition) indexes are written to your BIOS (SPI chip) directly by your OS installer.

UEFI is not quite stable (especially on notebooks) where more than one OS installed, UEFI records can create clutter and lead to bios corruption or boot lockdowns, only way to fix would be reflashing eeprom chip (generally same chip where your BIOS software is) or replacing it (I've personally experienced.) as a result, Legacy (MBR) mode installations are "safer" (maybe biased) over EFI.

Vishukani
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