I used to develop windows shareware, all the way back to Windows 95. Back then you could write to the installation folder "c:\program files\myapp" and life was simple.

At some point MS figured this was bad security, and you needed to write to the Windows Rigistery (HCKLM / HCKLU) to store your app settings. And write to C:\Users\<username>\AppData\ folder to store your data files.

So all of this resulted in 3 different places you needed to write your data to now. But then it gets even more split because, in some cases you needed to run as an admin during the installation, and your appdata will be stored under the admin account. Also, at some point c:\progrm files\ was split, and also they added c:\program files (x86), and I believe the c:\program files\ is virtualized. And the Windows registry is also split for local user, and machine settings, and admin settings.

Two issues I ran into:

1. c:\program files\myapp\ I could not trust what I wrote there. I believe its virtualized. So I ran into issues where I would delete a file in my installation folder, and old version would be put back by windows in the background.

2. When a regular user installed my app, and it need to write to HKLM, the app will need to be elevated to admin to be able to do that. This also resulted in another split of settings. Because there are per user settings and per machine settings.

In conclusion, app installation became a confusing mess!