Startup Sequence For Windows PE

Question

Hi Everyone,

I am hoping someone here can answer a question for me. What is the bootup sequence for a WinPE? what file and or command line starts the boot process. It's pretty cut and dry when you're running a Windows program, but not so much when it comes to a PE. There are no exes that I can see inside the ISO. I'm trying to understand what happens because I'm trying to reconstruct an multiboot USB file system. The tool I used failed to create the menu that would have allowed me to select the program that I want to execute. My setup contains the files found in each rescue ISO. Each set of files is contained in its own sub directory. I need to create a menu with entries for each of the programs and the command line to execute when I select a program. The programs are Partition Assistant, Macrium Reflect and a Windows AIO. Here are some screenshots to help show the layout of the file system.

I have looked online for an explanation of the boot process and I have not been able to find anything.

the Root

the Programs diectory

The program execution would be something like:

1. ISO boots showing menu of choices.
2. User (Me) selects an option from the menu.
3. Go to that program's directory and execute the commands needed to start the program.

I'm not asking anyone to solve the who problem. I just want to understand the boot process for a PE so I can try to solve it myself. I would be grateful for any help you can provide.

***moved from Windows / Other/Unknown / Performance and system failures***

Answer 1

Hello V. ShaneCurtis,

thank you for posting on the Microsoft Community Forums.

To better understand the boot process for a WinPE (Windows Preinstallation Environment) and create a multiboot USB setup, let's break down the essential components and sequence:

1. **Initial Boot Process**:
   • The process starts with the BIOS/UEFI firmware, which loads the bootloader from the bootable USB drive.
   • The bootloader (could be bootmgr, bootmgr.efi, or a custom bootloader like GRUB) is responsible for initiating the boot sequence.
2. **Bootloader Execution**:
   • If GRUB is used, it will read its configuration file (grub.cfg) to present a menu of choices to the user.
   • If bootmgr (Windows Boot Manager) is used, it will look for the BCD (Boot Configuration Data) store to present boot options. This may be less flexible for a multiboot setup.
3. **Menu and Selection**:
   • You design the menu (in grub.cfg) with entries pointing to each of the subdirectories containing the rescue ISOs.
4. **Executing WinPE or Program**:
   • Once a selection is made, GRUB loads the corresponding files from the subdirectory and transfers control to the appropriate boot file.

Hope it helps.

Best regards,

Lei

Answer 2

Thank you for your reply Lei. Could you possibly direct me to someone who could answer questions about how to boot a windows PE ISO from a GRUB menu. I have looked everywhere searching for the commands needed to boot a windows PE from a GRUB menu without success, The PEs I'm trying to boot are rescue ISOs such as Macrium Reflect, Partition Assistant and a few others. I would also like to find instructions about how to manually create a PE and add programs to it. Specifically, I want to add the MS Office install to a PE so I can create a bootable ISO image that can be added to Ventoy.

Thanks in advance