Here[1] is a short video showing the version by version upgrade of Windows 1.01 to Windows 8. Notice how essentially all user programs, system preferences (e.g., theme), and files are preserved throughout the entire process. The guy also runs an installed copy of Wolfenstein 3D on almost every version to demonstrate that it still works.

The first time I saw it made me respect and appreciate the stability Windows has provided over the decades...

Note: there are similar videos that show the exact same process on actual hardware.

[1]: https://www.youtube.com/watch?v=vOzkNtnaS04