DOS ain't dead

Cannot boot DOS on ASRock B850M Pro with CMS from USB (Users)

posted by RayeR , CZ, 03.09.2026, 00:23

I had a chance to play for a moment with relative new PC at work ASRock B850M Pro with AMD Ryzen 7 8700G with Radeon 780M IGPU so I tried just boot DOS from USB stick. I still can find CSM enable option in SETUP but it didn't work. I just got a black screen with white cursor on top (non-blinking). When CSM enabled there appeared another option: Launch video OpROM Policy: UEFI only|Legacy Only|Do not launch. So I changed it to Legacy Only but it hanged during POST with a black screen I even cannot enter SETUP anymore - have to reset CMOS. Then I read that AM5 CPU's IGPU completly dropped legacy VGA BIOS so no chance. As last resort I tried to put there an old PCIe GeForce 730 but still cannot boot DOS, Legacy Only option behaved the same. In UEFI mode I can boot UEFI shell and other stuff from that USB stick. So beware that CSM option doesn't always mean it could boot DOS...

---
DOS gives me freedom to unlimited HW access.

Complete thread:

• Cannot boot DOS on ASRock B850M Pro with CMS from USB - RayeR, 03.09.2026, 00:23 (Users)
  • Cannot boot DOS on ASRock B850M Pro with CMS from USB - FFK, 03.09.2026, 11:30
    • Cannot boot DOS on ASRock B850M Pro with CMS from USB - RayeR, 03.09.2026, 14:21
      • Cannot boot DOS on ASRock B850M Pro with CMS from USB - FFK, 03.09.2026, 17:16
        • Cannot boot DOS on ASRock B850M Pro with CMS from USB - RayeR, 07.09.2026, 19:39
  • Cannot boot DOS on ASRock B850M Pro with CMS from USB - samwdpckr, 05.09.2026, 13:25
    • Cannot boot DOS on ASRock B850M Pro with CMS from USB - Laaca, 05.09.2026, 18:06
  • Another legacy boot attempt on Gigabyte B850I Aorus Pro - RayeR, 08.10.2026, 23:01
    • Another legacy boot attempt on Gigabyte B850I Aorus Pro - Zyzzle, 09.10.2026, 09:40
      • Another legacy boot attempt on Gigabyte B850I Aorus Pro - RayeR, 10.10.2026, 05:41