Hey there morac68!
I've found an article that will explain a little more about the restore process to you:
Specifically, this sentence gives you the answer you are looking for:
Restoring your device will delete all data and content, including songs, videos, contacts, photos, and calendar information, and will restore all settings to their factory condition.
As it says later on in the article, you may want to follow these steps before restoring:
Thanks for using the Apple Support Communities!