UEFI Enabled Install

Guys, I'm confused...again haha!

Some of these Windows 7 machines have UEFI to some extent. At least they have the option for Secure Boot and Switching Off UEFI, and just use Legacy. My issue is, when I go to install to a machine that came with Windows 7, but had the Windows 10 Upgrade, I don't know if I can chose the UEFI Entry at boot or not?

The last one I installed in Legacy, but UEFI was Enabled. The OS would not boot so I Disabled UEFI and all booted fine.

My Main Question at this point is: Is it even possible or suggested to Install from the UEFI Boot List, and therefore leave UEFI/Secure Boot Enabled? I ask because the UEFI Boot List is always Enabled even though the pc came with Windows 7. Both these machines came with Windows 7 and had Windows 10 Upgrades via the usual Forced Upgrade lol, just kidding. Whew, hope all that makes sense.

The basic idea of uefi and secure boot is the system will only boot a o/s that's registered so any virus that changes system boot files will be stopped and it prevents anyone booting another system to access the PC

Thanks samuria, but I understand UEFI, I just don't understand why it is Enabled on a Windows 7 machine? And, refer again to my opening post please in case you did not read it.

As Samuria mentioned, with Secure Boot enabled, during boot bios look for a digital signature on on the boot loader. Win 8x, win 10 and Linux can use Secure Boot. Win 7 can't.
- You have two kinds of BIOS operation: Legacy - MBR and UEFI-GPT.
- If BIOS is set to Legacy - MBR operation, the boot sequence start on BIOS that looks for a MBR on a DISK (boot priority). From the MBR the boot sequence is transferred to a master boot loader on a Partition (same disk or not) that can call a boot menu (multi boot) that can transfer to another boot loader. For ex Grub (master boot loader) that can call Linux boot loader or windows boot loader.
- If BIOS is set to UEFI - GPT operation, the boot sequence start on BIOS that looks for a boot loader on a Fat32 partition that will call the OS on a partition. On this Fat32 partition you can have endless independent boot loaders, each one calling a different OS on different partitions (same disk or different disk).

As you can see, if BIOS is set to operate as Legacy - MBR you must have the OS on a Legacy - MBR disk and if BIOS is set to operate as UEFI - GPT you must have the OS on a UEFI - GPT disk. One isn't compatible with the other.

Win 7 64 can boot from a UEFI - GPT disk.

- BIOS should have two operations modes: Legacy - MBR OR UEFI - GPT
- Secure boot: Enabled or Disabled
- Fast boot: Enabled or Disabled

Some manufactures (like Asus) made a big mess when referring win 10 as UEFI.
So it has two operations modes: UEFI and other (UEFI = Win 10 UEFI w/ secure boot, Other = secure boot off)

When operation mode= Other you can still have:
CSM (Compatible System Mode): enabled=Legacy - MBR
CSM (Compatible System Mode): disabled= UEFI - GPT
Secure boot: Enabled or Disabled

If the original Win 7 was installed in one operation mode, when you downgrade to win 10 it will be installed on same mode.

Nasty7 said:

The last one I installed in Legacy, but UEFI was Enabled. The OS would not boot so I Disabled UEFI and all booted fine.

I understand most of that, what I don't understand is why the last machine was UEFI Enabled, even though it had Windows 7 from the OEM, and I assume no one had messed with it, guess I should not assume.

I guess the answer is Windows 7=Secure Boot NO!