The bootloader must enable the A20 gate, configure a GDT and an IDT, switch to protected mode, and for x86-64 CPUs, configure paging and switch to long mode. On a legacy system, BIOS performs all the usual platform initialization (memory controller configuration, PCI bus configuration and BAR mapping, graphics card initialization, etc.), but then drops into a backwards-compatible real mode environment. The differences are in where they find the bootloader/OS, how they prepare the system before executing it, and what convenience functions they provide. In reality, both legacy motherboards and UEFI-based motherboards both include BIOS ROMs.

Use the OVMF-blobs repo or download the RPM version, then use 7-Zip File Manager to extract the OVMF.fd file from the downloaded archive.Ī common misconception is that UEFI and BIOS are mutually exclusive. Under Linux, you can also install these with your distro's package manager, for example:

RPM packages (official TianoCore packages).

OVMF-blobs (unofficial precompiled 32 bit and 64 bit versions, easy to use).

It might be tricky to find, so here are some alternative download links too: Otherwise for emulation and virtual machines, you'll need an OVMF.fd firmware image. You just have to enable it in the VM's preferences by clicking 'Settings' / 'Systems' / 'Enable EFI (special OSes only)' checkbox. If you choose VirtualBox for virtualization, then UEFI is already included, no need to download the image manually.

7.2 My bootloader hangs if I use user defined EFI_MEMORY_TYPE values.

7.1 My UEFI application hangs/resets after about 5 minutes.1.3 Legacy bootloader or UEFI application?.

Efi shell commands boot