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Create a Custom ISO for Windows 10 -- Part 6 of 6

By Kari the Finn, guest blogger for Ed Tittel, courtesy of

Note: this blog is Part 6 in a series of 6 parts on the topic of using Sysprep to craft a custom ISO for use in installing Windows 10, aimed at the upcoming Creator’s Update scheduled to become available in mid to late April. Your guest blogger for this series is Kari the Finn, well-known Windows Install expert at He’s the person who put tools together (ESD2ISO and UUP2ISO) that let savvy installers convert Windows OS download files into ISO images that may be used to create bootable installation optical media or USB Flash Drives.

Part 1 covered the intro, and Part 2 started users with installation prep; in Part 3 you learn how to update and customize Windows; Part 4 dug into generalizing a Windows image using the Sysprep utility; Part 5 described how to capture the generalized Windows image and turn it into an installable ISO. Here in Part 6 we conclude by explaining how to update or change that ISO file over time. Don’t let the numbering bother you (Part 1 was an introduction, so step 1 of Kari’s 5-step process appears in Part 2, step 2 in Part 3, and so on…) Here’s Step 5/Part 6:

5. Update / Change ISO

The beauty of using Hyper-V VM as technician machine lies in how easy it makes the job of maintaining and updating a customized install image. I am a Fast Ring Windows Insider. That means I get new pre-release builds frequently and thus, want to upgrade my ISO at the same pace. I’m too lazy to go through this whole process weekly (or more often). The same holds true if I no longer want my custom image to include certain pre-installed software elements, want to update or add new software, or want to change the desktop theme or whatnot.

When I feel like changing the ISO I simply apply the Hyper-V technician virtual machine’s standard checkpoint I created just before sysprepping Windows. I can add and remove software, update software, run Windows updates, apply a new theme, or do whatever else I might want to.

When that’s done, I run Disk Clean-up, create a new checkpoint to be able to restore to this point, and repeat Sysprep, capture a new install.wim and make a new ISO. It’s much faster now. The whole process takes just minutes, because both Windows and basic software are already installed.

Upgrading the Custom ISO

As a Windows Insider I might also be interested in upgrading my ISO. When a new build arrives, I restore the checkpoint I created when the technician machine was fully setup after capturing the install.wim file. I can’t use the checkpoint made in Audit Mode before Sysprep because upgrading Windows in Audit Mode is not possible.

Now, booted to normal mode I can upgrade to the latest Insider Build or the next Feature Update Build using Windows Update or a standard ISO image. When that upgrade completes, I enter the following command in an elevated Command Prompt to restart Windows in Audit Mode:

%windir%\system32\sysprep\sysprep.exe /audit /reboot

Windows restarts, then signs into Audit Mode using the built-in Administrator account. The next thing to do now because my initial user account already exists is to open Settings app > Accounts > Other users and delete all existing user accounts also removing their profile folders. I also delete the custom made install.wim file from last time if it’s still located on the image drive (E: in this example) and check to ensure that the Scratch folder still exists (if not, it must be re-created manually as described in Part 4 of this 6-part opus).

Now a Disk Clean-up, Sysprep, capturing install.wim once again and finally writing a new ISO. That’s it!

For Further Questions or comments…

If you have any questions about this 6-part series, or comments to share, do not hesitate to contact me! Here’s my information:

Kari Finn

Links to All Series Elements

Part 1: Introduction & Overview
Part 2: Install Windows and Prepare Assets
Part 3: Update and Customize Windows, Install Software
Part 4: Generalize Custom Windows Image with Sysprep
Part 5: Capture Custom Windows Image, Create ISO
Part 6: Update/Change Custom Windows ISO

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Great series from part 1 to 6. I obtain my Windows 10 Creators Update ISO files AND I will do as mention in this for Custom ISO for Windows 10.
Thanks for this awesome step by step. Being a total newbie at this, it came in super handy.  I have setup a Vm to test this new image I just created, and it appears to work well, but I might have missed something.  So I created a new VM, booted with the ISO created per steps above, and Windows has been installing for a while, and reached a point where it checked for updates and is now downloading a 4gb updates (or so it says).  This is obviously not ideal. I thought the update would have been part of the ISO.  I've re-read the whole tutorial, but can't quite see where I messed up. Someone more knowledgeable can point me to the right direction? 
Thank you Kari for this great tutorial! You helped me a lot.
Thank you very much for this great tutorial! You helped me a lot.

great tut, Everything worked fine, except when I try to run setup.exe of the custom image, it starts fine but then I get the error 'setup has failed to validate the product key' I have tried creating a custom image using our volume purchasing version of Win10 Pro and also a consumer using Microsoft Win10 downloader, but both get the same error. anyone have any thoughts on this? where are people getting their copies of Win10 that they are using for this process?

p.s. I also never get a screen during the setup process asking for a serial(that the instructions say to skip), so maybe it has something to do with that also?


Hi, I get the error 'Setup has failed to validate the product key' when running setup.exe on the custom ISO. I've tried a volume purchasing copy of Windows and a downloaded Win10 pro using the Microsoft downloader. any thoughts? where are other people getting their install media? Also during the creation instructions I never saw the stage where it asks for a serial number, that the instructions say to skip.
@realm174: 4 GB updates sounds incredible, without more information I cannot explain it.

However, I've written a tutorial about updating Windows install media (ISO or USB) to keep your custom ISO always up to date. Please see the tut:

@Hcril01: The error you are getting is only possible when autounattend.xml does not contain a generic product key and can't continue. Creating autounattend.xml is not covered in this series, please refer to this article:

You can also contact me at ten Forums: