Does Apple TV only work with a Laptop or PC/Mac on or will an external HDD work on its own?

I'm thinking about buying Apple TV. I'm to decide on a generation.

I currently run a laptop (non-apple). I'm going to be buying a Network Hard Drive (WD) I believe the drive is iTunes compatible. So my questions is...Do I need to have my laptop on in order to use Apple TV to view photos, play music etc. or if I transfer the photo's and music to the WD HDD will that be enough?

So I can use Apple TV without my laptop being on at all, provided I configure Apple TV to the HHD?

If my question is stupid I'm sorry but I'd appreciate an answer and other threads aren't very clear to me infact some are providing conflicting information.