The Grub2Win Boot Process
Notes on how it works
EFI Mode
For All Windows Versions Running On EFI Firmware Systems
At boot time, the EFI firmware in your PC loads the customized GNU Grub EFI Boot Manager module.
For 64 bit systems, the module is /EFI/grub2win/g2bootmgr/gnugrub.kernel64.efi
For 32 bit systems, the module is /EFI/grub2win/g2bootmgr/gnugrub.kernel32.efi
The GNU Grub EFI Boot Manager then takes control and performs the following actions:
Searches all disk drives for file /grub2/g2bootmgr/gnugrub.functions.cfg to find the partition where the Grub2Win base directory is installed.
This is usually the Windows boot partition C: drive.
Sets variable $grub2part to the address of the partition where Grub2Win is installed.
Sets variable $prefix to the Grub2Win partition address followed by /grub2.
The $prefix variable is required by grub2 to locate its base directory and files.
If $prefix is not set properly, grub2 initializes in rescue mode (limited command line).
Loads several other GNU Grub modules to support various partition and filesystem types as well as USB drives and keyboards.
Reads file $prefix/grub.cfg and builds the grub2 boot menu display.
This is usually file C:\grub2\grub.cfg
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BIOS Mode
For All Windows Versions Running On BIOS Firmware Systems
The Windows MBR loads the customized Grub2Win Boot Manager module.
For Non-XP systems, the module name is /bootmgr see the BCD Flowchart
For XP systems, the module name is /ntldr see the XP Flowchart
These modules reside on either your C: drive or your "System Reserved" partition.
The exact location depends on the disk configuration when Windows was installed to your machine.
The Grub2Win Boot Manager module then takes control and performs the following actions:
Searches all disk drives for file /grub2/g2bootmgr/gnugrub.functions.cfg to find the partition where the Grub2Win base directory is installed.
This is usually the Windows boot partition C: drive.
Sets variable $grub2part to the address of the partition where Grub2Win is installed. Usually (hd0, msdos1).
Sets variable $prefix which usually has a value of (hd0, msdos1)/grub2
The $prefix variable is required by grub2 to locate its base directory and files.
If $prefix is not set properly, grub2 initializes in rescue mode (limited command line).
Loads several other GNU Grub modules to support various partition and filesystem types as well as USB drives and keyboards.
Reads file $prefix/grub.cfg and builds the grub2 boot menu display.
This is usually file C:\grub2\grub.cfg
If you select Linux or another non-Windows operating system, Grub2Win loads the appropriate bootloader.
If you select Windows, Grub2Win loads the Microsoft Windows Boot Manager module.
For Non-XP systems, the module name is /microsoft.bootmgr.bios
For XP systems, the module name is /microsoft.ntldr.xp.bios
The Microsoft Windows Boot Manager now takes control and loads Windows.
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