As you likely know, while one can install Windows 7 from an external hard drive, one can’t install the same to an external hard drive with default settings. For all those users waiting for a good workaround to install Vista, Windows 7 and Windows Server 2008 R2 to an external hard drive, here is the complete solution.
Even though Windows recognizes and displays the USB hard drive in the installation screen, it doesn’t allow you install Windows on the same. When you attempt to install Windows 7 on external drive, you get “Windows cannot be installed to this disk” error.
So, if you want to install Windows 7 on an external hard drive you need to follow the steps given below. The procedure is simple but you need to install Windows Automated Installation Kit (WAIK) first to get some files. We would like to thank fujianabc @ boot-land forum for this workaround.
# An external hard drive formatted with NTFS
# Windows 7 installation files (if you have Windows 7 ISO use Virtual Clone Drive freeware to mount it)
# Windows Automated Installation Kit (free download from Microsoft)
NOTE: Make sure that you have a minimum of 15 GB free space on your external hard drive before starting the procedure. Although we are not going to delete the contents of external hard drive, we recommend backing up your external hard drive contents before trying this guide.
Step 1. Create two folders named Windows Files and WAIK Files on your desktop or any other drive which has a minimum of 5 GB free space.
Step 2: Download the ZIP file from here and extract the contents to WAIK Files folder. Before starting the actual installation procedure, you need to have three files: Bcdboot.exe, Bootsect.exe and Imgex.exe. These files can only be obtained by installing Windows Automated Installation Kit for Windows 7 on your Windows PC. After installing WAIK, simply search for these files in the Windows installation drive to get them. Once you have these three files, copy them to WAIK Files folder that you have created in the above step.
Step 3: Copy all the contents of Windows 7 installation DVD to the Windows Files folder.
Step 4: The next step is to run Installer.cmd file as Administrator (Right-click on installer.cmd and select run as administrator). In the first screen, you will be asked to press Enter to continue.
Step 5: Press Enter key to browse to the install.wim file present in the Windows Files folder. The Install.wim file can be found under Sources folder (Windows Files/ Sources/ install.wim).
Step 6: Now, you need to select the Windows 7 edition that you want to install on external hard drive. You can select the edition by entering the index number shown in the screen. For example, type “5” (without quote) and hit Enter key to select Ultimate edition.
Step 7: The next step is to enter your External drive’s drive letter. Enter the drive letter (ex: L) and press Enter key.
Step 8: Now, type in the drive letter of your ACTIVE partition and hit Enter key. Generally “C” is the active partition. You can find the active partition by opening Windows Disk Management tool (type diskmgmt.msc in Start menu search area and hit enter to launch it).
Step 9: Finally, the installer will ask you the drive letter that you have entered to install Windows 7 is a USB hard drive or not. As you are installing Windows 7 to an external hard drive simply type “Y” without quote and press Enter key.
Finally click Enter key again to start extracting the Install.wim files. This might take a few minutes. Once done, you will be asked to reboot your PC to continue the normal Windows 7 installation procedure.
Step 10: Reboot your PC and follow the usual Windows 7 installation procedure to complete Windows 7 installation on external hard drive. Your PC will be restarted twice or thrice during installation.
Please note that the installation procedure might be slower as you are installing Windows 7 to an external hard drive.
Step 11: Once done with the installation, you are good to go. You can install all drivers and other software to start using the best Windows version on your PC.
Note: We have tested this method to install x86 flavor of Windows 7 to Seagate USB external hard drive. But should work fine with x64 as well. Users who would like to carry Windows 7 on a USB flash drive can follow our how to carry Windows 7 on USB flash drive guide.