@TKoller said in .data folders:

can anyone explain what these folders are and why they are only on my friends pi?

Maybe you can ask your friend, since they're the one that set it up. RetroPie doesn't provide any ROMs, so they must have been added after the installation.
If I had to guess, they've used the .data folders to hide certain files from being displayed in the gamelist - a common method when you have a multi-disk game and you want to show just a single entry for the game (i.e. create a .m3u file pointing to the individual disc files placed in the .data folder).

@iandaemon Custom Collections is exactly what I was looking for! Thank you.

@nevisx Think about using favorites on ES. There you can collect your files so maybe a list with NES translations and NES Homebrew will help you. Real folders are not intendent to work .......

There is a bug in ES that makes folder navigation possible.
https://retropie.org.uk/forum/topic/11308

But it needs modified scripts to define right emulator calls - from the edge view it is possible with lots of manual editing gameslist files.

@yussafm Good questions. Easy to try a few tests on your own, as not everyone is using it the way you propose. My advice is to avoid folders by letter, as Emulation Station lets you easily jump directly to letters, you can page up page down, and with recent enhancements, there are many ways to build your own custom game lists (and using that technique, you could add favorites, make lists by letter, etc.).

As for timing, I think you will have to do some of your own tests. There are factors like your SD card speed (or whatever you are using to store your ROMs). I would expect it to affect boot times somewhat, as the ROM lists are gathered, but you will have to try it and find out if it's acceptable for your needs. Maybe someone else will reply with their specific examples. My loads are very fast, but I only have a few hundred ROMs.