CSM disabled vs CSM -> all UEFI only

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   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.

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keeka Members Profile Send Private Message Find Members Posts Add to Buddy List Newbie Joined: 22 Dec 2015 Status: Offline Points: 30	Post Options Post Reply Quote keeka Report Post Thanks(0) Quote Reply Topic: CSM disabled vs CSM -> all UEFI only 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.