How to legally generate the Windows ISO from a Mac or Linux PC

27 May 2015

Surprisingly, it turns out that getting your hands on a legal Windows ISO after purchasing it is not as easy as it might seem. After purchasing a digital copy of Windows in the Microsoft store, you will be able to download a Windows application that downloads the ISO for you after entering your product key.

Therein lies the issue: to create a Windows install media, you need access to a PC with Windows already installed. If like me all you have on hand is a Mac or Linux PC without easy or quick access to a PC with Windows (or one that you can trust with your product key), you are left in a tight spot. Even the Microsoft support will not be able to help you and will simply point out that it can’t be that hard to find a PC with Windows.

Worse still is that not all versions of Windows are supported and for example, all versions that run on the Free Amazon Web Services are not supported so this avenue is not open to us either (at least at the time of writing).

The only viable alternative appears to be to download the ISO from an untrusted torrent site. If like me this leaves you uneasy, read on.

As it turns out, an unrelated tool that Microsoft releases will allow us to execute that ISO generating executable in a safe and legal way.

Step 1

Install Virtual Box. Virtual Box is a virtual machine application from Oracle that allows you to run an operating system in a virtualized environment as a guest.

Step 2

Download a Virtual Box image from the Internet Explorer Developer website. These images are legal versions of Windows provided by Microsoft to allow developers to test various Internet Explorer versions on various Windows versions. They expire after 90 days and cannot be activated but that doesn’t matter to us since we’ll only really use it for as long as the download of the ISO takes.

Simply grab the image for the platform that you have (Mac or Linux). Note that most images are 32 bit which will only allow you to later download the 32 bit ISO. At the time of writing, the Windows 10 image is 64 bit but requires the following fix to work properly.

Step 3

Inside Virtual Box, import the Windows image downloaded at the previous step. The documentation recommends you set at least 2GB of RAM for the virtual machine to use. This is fine since we’ll only run it for a short amount of time anyway.

Step 4

Use Virtual Box to share a directory with the virtual machine with write access and make sure it automatically mounts (easier for us). This is the directory where we will copy the ISO file into. At the time of writing it does not work with the Windows 10 image yet and as such you will need to plug in a USB key and share it with the virtual machine from the settings or share a network folder (I had more luck sharing the folder inside the Windows guest virtual machine and accessing it from my Mac).

Step 5

Launch the virtual machine instance and use it to run the executable from the Windows store. If you do not have access to it, I have not tested but presume that you might be able to use this utility as well.

Step 6

Follow the instructions and download the ISO to some directory (e.g: the desktop). For some reason Virtual Box did not allow me to download directly to the shared directory we setup in Step 4. Either way, once the download terminates, simply copy the ISO to the shared directory.

Complications

Sadly, the Windows 10 image is a bit finicky. You can’t shutdown properly and install the updates or it won’t boot again and you’ll have to start over. I could not manage to get my USB stick to work either and as such I had to create a shared directory inside the Windows guest. In order to be able to access the shared directory, I had to hot swap the virtual machine network card from NAT to Host bridge (you will need to add a host adapter in the Virtual Box preferences). I also needed to add a default gateway in the IPv4 settings of the Windows guest for my mac to be able to access it and I also needed to allow Guest access in the network settings.

Next, due to our previous hack to change the time to allow Windows to boot, the executable will refuse to download the ISO and complain it can’t connect to the internet. To resolve this I had to change the time inside the guest manually to the current date. I also needed to hot swap the network card back to the NAT setting and removed the default gateway.

Last but not least in order to copy the ISO out, I had to hot swap the network card once again to Host bridge and add back the default gateway.

Profit!

That’s it! You are done and you can now get rid of Virtual Box if you wish to. You can now continue the steps to create your bootable DVD or USB stick from the ISO.

There are so many threads out there asking how to do this that I hope this will be able to help someone avoid the hassle I went through to find this. You would think Microsoft would make it easier for you to install their operating system…