@infarmer8 sagte in PrettyOS inside coreboot/SeaBIOS as a virtual floppy! - Stuck while booting at "Switching to Protected Mode (PM)..._": What might be the reason that PrettyOS got stuck at "Switching to Protected Mode" ? Sadly this problem isn't reproduced at QEMU or VirtualBox, but I could help you to debug it, waiting for your instructions Did you try the boot process with other real computers? You could look up the assembler code of the second stage bootloader: https://sourceforge.net/p/prettyos/code/HEAD/tree/trunk/Source/stage2_bootloader/boot2.asm line 77 ff. Perhaps you could check code/data selectors with your system?