The phone memory (system data card data like images, videos, contacts) is stored on server or not?
After hard reset data is gone so that is stored someone else or in databases?
No, it is not stored anywhere.
You should create your own backup manually. After hard reset, even the game data would be deleted.
The only data you can have left with you is the data you have already synchronized with google.
No, the phone memory isn't stored on a server, but there are some easy-to-use (and built-in) ways of backing up different kinds of data.
If you save contacts to "Google contacts" instead of "Phone contacts" when you create them, they're synced with your Google account, so they'll automatically be synced to your new phone, or after a factory reset, when you sign into the same Google account. The same applies to calendar events, if you add them to a Google calendar.
Android phones have a built-in backup system, which backs up apps' data to Google's servers. All you need to do is turn it on in the phone settings, and make sure the "Restore my data" checkbox is checked when you sign into the same Google account on the new phone, or after a factory reset. This only backs up data from apps that support it. Check with the developer of each app! It doesn't back up photos, music, &c. from the SD card.
To back up photos, use an app with a "photo upload" feature, such as Google+ or Dropbox. Once you've turned the feature on, it'll automatically upload each photo or video as soon as you take it.
If you don't do any of these things, then when you factory-reset your phone, everything on it is gone.