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Old July 5th 18, 12:57 PM posted to alt.comp.periphs.mainboard.asus
Bill Anderson
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Posts: 249
Default SOLVED: Problem with Asus Prime X299-A UEFI BIOS

On 7/4/2018 11:04 PM, Paul wrote:
Bill Anderson wrote:
I'll post this even though I'm not convinced anybody who can use the
info will ever find it here.Â* It's just that I've received so much
good info in this newsgroup over the years (primarily from Paul) that
I want to give back if I can.

My problem was that I'd installed three versions of Win10 on my new
Prime X299-A setup and when I'd choose something other than my default
OS using F8, all the boot options (OSs and optical drive) would get
scrambled in UEFI BIOS. Once I'd picked an alternative OS using F8, I
never could be sure exactly what OS I'd get upon reboot. (I don't use
Boot Manager, want never to see it.)

I explained this problem today to a tech via the Asus website chat
feature and this is how he replied:

This should do it:

1. Disconnect all the other drives from the unit leaving only the main
boot drive.
2. Go to BIOS and under boot then go to OS type and set it as Windows OS.
3. Disable Launch CSM.
4. Save and Exit the and this should lock it as the boot device.

After this you can add back the other drives and try the F8 option and
see if it fixes the issue.

Yes, I had to do a little investigative digging to find a way to set
OS type as Windows OS, cuz the option wasn't exactly where he said it
would be, but that's OK. Bottom line is that this worked: Now I can
pick the OS I want by using F8 without worry.

And the takeaway is that Asus Tech Support came through for me on the
first try. Yay!


I find

Â* powercfg /h off

works for me. This prevents both hibernation and Fast Start,
so that the BIOS F8 selection process will be an honest one.
I can leave CSM enabled.

Of course, if you're a big hibernation person, that'll be
an issue for you.

EasyBCD could be used to add the other OS drives, then leave
the BIOS configured to boot the "boss" drive. But that doesn't
cover every usage scenario, so won't keep everyone happy.

UEFI has a relatively large NVRAM storage facility. Likely
using the BIOS Flash chip for the actual storage. It can
memorize environment variables. By comparison, traditional
BIOS only have the 256 byte CMOS storage. And using CSM mode
is an emulation of a traditional BIOS.

Intel has declared CSM to be a dying feature, so
in a few years, motherboards will be UEFI only.
We'll have to wait and see, as to whether the rest
of the industry agrees.

Â*Â* Paul


I think I'm about to learn something basic.

I don't understand how making an adjustment in Windows can have an
effect on which of three Windows installations BIOS chooses to boot
from. Isn't the choice made prior to the computer seeing anything in
Windows?

I do know that when Windows is installed using UEFI, I don't choose an
actual HDD/SSD using F8, even though F8 lists them as choices. Instead
the choices that work are all labeled "Windows Boot Manager" followed by
the physical location of the installation. It's easy enough to identify
the drive I want that way. But it's obvious UEFI/BIOS knows it's
looking at Windows installations, so maybe it's picking up some Windows
data even prior to booting from a particular drive?

And if I tried your suggestion, wouldn't I have to make the same entry
in all three Windows installations?

--
Bill Anderson

I am the Mighty Favog