CSM/MBR boot on Taichi

claude.rivet wrote: Hello, I am trying to setup my BIOS for CSM/MBR booting rather than UEFI, it is required by Grub4dos and I need that bootloader. I cannot find where I can specify if boot is UEFI or CSM/MBR, anyone can help? Thanks, regards

Very simple answer. With CSM enabled (the default setting) you will get MBR formatting and booting, at least that is how it works in Windows. I don't think it will be any different with any version of Linux.

With CSM enabled, all the sub-options will be set to Legacy Only, which will cause MBR booting.

Setting CSM to disabled, or with CSM enabled, setting the Launch Storage OpROM policy to UEFI Only, causes GPT booting/formatting. The terms MBR and GPT are not mentioned, but I assure you that is how it works.

ASRock always set the default value of the CSM option to Enabled, and the CSM sub-options to Legacy Only. That always causes MBR formatting and booting, the default behavior when CSM is enabled.

Disable fast boot and enable CSM


You could press F11 before BIOS posts to get the boot selection menu.


2 disk's shown here with a choice of either legacy (in red box) or UEFI boot.  Choose legacy. Note that with CSM enabled and legacy devices (storage / graphics) one can still boot a GPT disk.

Personally I haven't used MBR partitioning on internal drives for years but from the sound of your other post it appears you have a GPT disk. The GPT contains a protective first sector that reports to any legacy system expecting MBR that the disk is fully used. If it's a disk you do not want to keep any data from then you could clear the first sector and create an MBR there instead.