UEFI Basics

When you enable UEFI on a computer how does it know that a device is capable of booting via UEFI? Is it looking for files or partitions on that device to identify it as being UEFI compatible?
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LockDown32OwnerAsked:
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Sushant GulatiConsultantCommented:
Easiest way to determine that you are booting through UEFI is when you see if you can disable the Secure Boot after pressing the F8 key after the POST.

https://www.quora.com/What-is-the-difference-between-UEFI-and-Legacy-Mode-which-we-need-to-choose-while-installing-the-OS

Here is the link where you can read the difference between both the booting modes, the Legacy and the UEFI.

Best,
~SG~
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LockDown32OwnerAuthor Commented:
Well.... if UEFI is set and enabled in the BIOS that pretty much guarantees that I am booting UEFI doesn't it? I need to revert to the original question.

I have notices when I press F12 (for a boot menu) only certain things show up. Only things that are "UEFI" compatible. How does it know if a device is capable for booting UEFI? Is it looking for files or folders on that device?
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Sushant GulatiConsultantCommented:
There are certain runtime checks that UEFI bootable devices make. For Ex:

1. It checks the Processor Compatibility that
2. It runs the Disk Device Compatibility also
3. EFI Services - like Boot and Runtime Services at the Firmware Platform
4. Graphics
5. EFI Protocols

When it comes to booting from UEFI, it does not rely on the Legacy Boot however it instead dependent on the boot manager part of UEFI.

On a UEFI system with Windows 10 installed, for example, the EFI file will be located at the following location, on that hidden partition:
\EFI\boot\bootx64.efi or \EFI\boot\bootia32.efi

On some Windows computers, the winload.efi file acts as the boot loader and is usually stored in the following location:

C:\Windows\System32\Boot\winload.efi

If there is no OS installed then from the DvD or from the ISO image the 2 locations would be

D:\efi\boot\bootx64.efi
and
D:\efi\boot\bootia32.efi

Let me know if there is something more I could help with.

~SG~
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LockDown32OwnerAuthor Commented:
That is what I was looking for. There is something on CDs, DVDs, Thumb Drivers, etc. That makes them UEFI bootable. It is the EFI folder and its contents. Thanks.
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