Intel Motherboards - CSM disabled vs CSM -> all UEFI only

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CSM disabled vs CSM -> all UEFI only

Printed From: ASRock.com
Category: Technical Support
Forum Name: Intel Motherboards
Forum Description: Question about ASRock Intel Motherboards
URL: https://forum.asrock.com/forum_posts.asp?TID=10357
Printed Date: 27 Dec 2024 at 11:45am
Software Version: Web Wiz Forums 12.04 - http://www.webwizforums.com

Topic: CSM disabled vs CSM -> all UEFI only

Posted By: keeka
Subject: CSM disabled vs CSM -> all UEFI only
Date Posted: 09 Dec 2018 at 2:47am

How does the behaviour of the motherboard differ between these two setups:

1. CSM disabled

2. CSM enabled plus Storage/Video/NIC each set to launch UEFI oprom only.

I was inclined to think these two configs would do the same.
However, they do not. I find I need to turn on CSM and enable UEFI video OPROM in order for windows 7 login and desktop to appear on dedicated graphics (with iGPU disabled). With CSM disabled, the screen does not get past windows boot logo, though the system is otherwise functional.
Also, with storage OPROM set to UEFI only, the F11 boot menu displays non UEFI boot disks as well as meaningless (to me) characters.
Doesn't make sense at all to me.
Motherboard: Asrock H170M Pro4
bios 7.2
CPU i5-6600
dGPU AMD RX 580

Hopefully someone can explain the difference between csm off vs csm on and all suboptions set to UEFI OPROM only.

Thanks.