#Grub2 windows 10 uefi bios windows#
Ordinarily, the Windows boot loader presents few or no options, although it can be configured to show a menu with some options. Now, to get to your question, it's not clear what tool was providing the functionality that has disappeared - it could be the computer's built-in boot manager, the Windows boot loader, or something installed as a custom boot manager by the manufacturer. Furthermore, some EFIs have bugs that cause them to forget or ignore their boot manager configurations. Thus, one computer may have a fairly decent user experience for its boot manager, but another may be hideous to the point of unusability. Unfortunately, the EFI spec includes NO guidance on what sort of user interfaces its boot manager should present. This functionality can be configured from Linux with the efibootmgr tool or from Windows with bcdedit or the third-party EasyUEFI.
![grub2 windows 10 uefi bios grub2 windows 10 uefi bios](http://www.billionwallet.com/windows10/images5/mbr2gpt1-2.png)
The critical difference is that the boot manager launches the kernel by using EFI system calls, as if the kernel were a boot loader - which it technically is.Īnother issue to keep in mind is that the EFI spec includes a minimal boot manager, which is built into the firmware, not stored on disk. Thus, a boot manager (like rEFInd or gummiboot/systemd-boot) can start looking a lot like a combination boot manager/boot loader, in that the boot manager launches the kernel. Since version 3.3.0, the Linux kernel has included a feature, called the EFI stub loader, that turns it into its own boot loader.My understanding is that it's still nearly useless on EFI-based computers.) (Windows tools like EasyBCD can help configure the Winddows boot loader's boot manager features, but I'm not very familiar with this tool myself. The Windows boot loader can also function as a boot manager, but it's more often configured to boot straight to Windows, so this functionality is less important - at least, when people set things up as Linux users generally do. GRUB, however, cannot directly launch a Windows kernel, so to boot Windows, GRUB passes control on to the Windows boot loader. GRUB presents a menu of options, like a boot manager but it can also directly boot a Linux kernel.
![grub2 windows 10 uefi bios grub2 windows 10 uefi bios](https://i.imgur.com/tDF0CXG.jpg)
Some programs, including GRUB, are both boot loaders and boot managers.This distinction is pretty simple and easy to understand, but there are some complicating factors that can make the difference seem rather blurry:
![grub2 windows 10 uefi bios grub2 windows 10 uefi bios](https://i.stack.imgur.com/7ee5K.png)
A program that functions exclusively as a boot manager does not directly launch an OS kernel, although the boot loader it launches will do so.