How To Easily Install Windows 7 & 8 onto An External USB Storage with PWBoot


Windows 8 introduced a new feature called Windows To Go that lets you put the entire operating system with your data onto a USB external device. Earlier, Windows 7 introduced a feature called Native VHD Boot that lets you set up a Windows 7 or 8 virtual that can directly boot without a host system. Building both systems aren’t so difficult but with a tool, it can be more simplified and easier. You can find the detail step-by-step instruction here and here.

Here is a post introducing an open source project called PWBoot (stands for Portable Windows Boot) that aims to simplify the process of making Windows Operating System to boot from any USB storage devices.

Things we need to start

Before we dive into the process, here are a few things we need to collect first:

  • A 16GB or up USB storage device. It could be just a USB key or an external hard drive. The more space it has, the better.
  • A Windows 7 or 8 computer.
  • Windows 8 installation media, DVD, USB, or just an image ISO file. If you only have the ISO file, mount it to Windows Explorer. What we need is a file named install.wim from the \source folder.
  • Last piece, of course, is the PWBoot portal executable file that you download from the open source project website.

Before you start the process

Because PWBoot will make changes to the BCD Store during the installation, it would be a good idea making a backup of your BCD Store prior to the process in case something happens unexpectedly.

To back up your BCD Store, launch Command Prompt windows as Administrator, and run the following command:

bcdedit /export "c:\bcd-backup"

Start the process

Double-click the PWBoot.exe file to launch the process. A wizard will pop up guiding you through the steps it needs to build the system.

PWBoot - step 1

Choose Install Windows, and go Next.

PWBoot - step 2 - select installation image

Click Browse to select the install.wim you have prepared in your Windows Installation Media. If the installation media contains more than one installation image, pick one from the second dropdown list.

PWBoot - step 3 - select disk partition

On setting up target window, you will have choices of selecting a physical device or creating one in VHD format. Either one would work so pick one and go Next.

PWBoot - step 4 - create VHD image

If it’s in VHD format, you will specify where you want this VHD file saved and how big it will be. Go Next once it’s all set.

PWBoot - step 5 - select boot partition for bcd records

Select a disk that host your BCD store and make sure the option Overwrite existing BCD store is not selected. Specify the description of this boot option and click Install.

PWBoot - installing windows

About 10 minutes later, you will have a bootable Windows system perfectly installed on your external USB device.

PWBoot will add a new boot entry to your BCD Store with the description you have specified in above step. You can run command bcdedit in Command Prompt window to confirm the new entry before restarting your computer to see the result.


PWBoot is a wonderful tool that makes your bootable Windows USB system a lot easier. When it works, it’s great. But when it fails, it could destroy your BCD Store to make your whole system completely unbootable. So it’s highly recommended making a backup of your current BCD store in case something go wrong.

I also recommend that you use PWBoot on a system that is not A Native VHD Boot system. In my own experience, I first used PWBoot on one of my Native VHD Windows 8 system, with a disaster result. It completely destroyed my BCD store, which took me a few hours to rebuild them back. But when I run it the second time on a normal Windows system, it works perfectly without any hiccups.

I also noticed one difference between this and Windows To Go. On a USB device I built using Windows To Go, I can boot it on almost any computer. But with PWBoot, it throws out an error that failed to boot when I tried to boot direct through USB without going through Boot Menu, which is weird.

/credit goes to Himanshu Sharma for this tip/


  1. Something here doesn’t seem right to me! why i need to update my own BCD if i’m not going to connect this portable OS into my laptop when my original purpose is to connect it into a PC/Laptopt with faulty/missing HDD or just keeping it as a fail safe contingency.

    Does it means that the portable OS has to have a cloned BCD from a good and running OS? and if in that case why there is no Sysprep stage in the step by step guide?

  2. Work for first starting. Everything ok. But then shutdown the computer and when start again
    I’m waiting long time and Windows can’t find ecplorer.exe etc problems.

  3. Great stuff. Just turned a thin desktop without an internal hard drive to run windows 8.1 on an external. Much appreciated!


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