Kobo Touch N905/B/C difference ?

Hello everyone!

I've just bought a Kobo Touch from WHSmith as they are £40 currently but I wanted to know the differences between the N905, N905B and N905C models?

I've read that the newer models had and internal SD card but what is that for? And are they more powerful or reliable?


Mine is N905 so I guess it's an old model ? I would not like to have a product which has been stored for 2 years...

Thanks for your help!

PS: Sorry if my english is not correct but I have an excuse, I'm french :)