Windows 8.1 is here at last, and all Windows 8 users can upgrade for free by visiting the Windows Store. Even users who are currently running the Preview code that was released in June can get the official update – something we’re very pleased to see, as it had been expected that they’d have to wipe their systems and perform a clean installation of the final code.

However, things aren’t quite as peachy as they may seem for Preview users. According to Microsoft’s own advice, if you installed the preview from the Windows Store, you’ll lose your applications when you move to the final code, and will have to reinstall them all. That’s a pain, and staying on the preview code isn’t a long-term option as it expires in January.

To carry out an in-place upgrade you’ll need an official Windows 8.1 installation ISO

There is an unofficial way to carry out an in-place upgrade, and keep your applications running. It doesn’t involve the regular Windows Store upgrade path: rather, you’ll need an official Windows 8.1 installation ISO, which Technet subscribers can download directly from Microsoft’s servers. Naturally, if you’re installing over a 32-bit preview installation, you’ll need a 32-bit ISO. If you’ve installed the UK edition of the preview, look for a UK-specific image. Enterprise users will need an Enterprise ISO. You get the idea.

The process we’re about to describe can be adapted to work with a DVD or an external hard disk, but the easiest way to proceed is if you can get your hands on a USB stick with a capacity of 4GB or more.

Making the change

The first step is to “burn” the ISO file onto this USB stick. There are plenty of free tools that can do this, including Microsoft’s own Windows 7 USB/DVD download tool. Note that simply extracting all the files from the ISO won’t do, as you need the device to be bootable.

Once this is done, go into the sources folder on the USB drive and edit the file called cversion.ini. It should look like this:

[HostBuild]
MinClient=9458.0
MinServer=9458.0

These numbers represent the versions of Windows from which this media will perform an in-place upgrade. The 8.1 preview was build 9431 – as you’ll know if you’re running it, since the build number is permanently stamped on the bottom right-hand corner of the screen. If the installer finds this edition of the OS on your hard disk you won’t be offered the option to upgrade. The solution is simple. Just change the values as follows:

MinClient=9431.0
MinServer=9431.0

Once you’ve made this change and saved the file, you can reboot your PC from your updated flash drive and follow the upgrade process, which will now be available.

Is it safe?

You might wonder whether hacking the installer like this is really a good idea. After all, Microsoft must have had some reason for disallowing this particular upgrade route. If you do follow these instructions, be aware that you’re doing something unsupported, and that there’s a chance that you might run into difficulties, either right away or with future updates.

Don’t worry too much, though. Early adopters used a similar trick to install the final release of Windows 7 over pre-release code, and no problems were reported. Since the 8.1 RTM ISOs were made available to developers in early September, preview users have been happily following the procedure above. So it seems that Microsoft’s disabling of in-place upgrades from preview code is a policy decision, rather than a technical necessity.

Darien Graham-Smith