How to upgrade from Windows 7 pre RC builds to RC

While waiting for the RC build, I just wanted to provide you with a little trick. By default only upgrades from Vista to Windows 7 RC is supported (So Microsoft get as much feedback as possible on the Vista upgrade scenario).

If you don’t have the time/incentive to wait for the downgrade to Vista and then an upgrade to the RC build (in my case I have three Vista machines and two Windows 7 machine that I will upgrade, so Microsoft will still get their feedback) then you can use this little trick -

Here’s what you can do to bypass the check for pre-release upgrade IF YOU REALLY REALLY NEED TO:

1. Download the ISO as you did previously and burn the ISO to a DVD. (See later comment)
2. Copy the whole image to a storage location you wish to run the upgrade from (a bootable flash drive or a directory on any partition on the machine running the pre-release build).
3. Browse to the sources directory.
4. Open the file cversion.ini in a text editor like Notepad.
5. Modify the MinClient build number to a value lower than the down-level build. For example, change 7100 to 7000 (pictured below).
6. Save the file in place with the same name.
7. Run setup like you would normally from this modified copy of the image and the version check will be bypassed.

These same steps will be required as we transition from the RC milestone to the RTM milestone.

The above is a snippet from from the Engineering Windows 7 blog post called Delivering a quality upgrade experience.

And of course in Step 1/2 you could just mount the ISO image using Daemon Tools version 4.30.4 (or higher) that supports Windows 7 and extract it to your preferred location.