DDK - Die Deutschen Klassiker

I bought a set of ATE Brake pads from Euro Car Parts. As I've put each hub back together and attached the calipers I've been fitting the pads. I just came to do the fronts tonight and found I have two different sets of pads left. Sure enough the ones on the rear are a different type on each side are different

Both sets are the same dimensions but one set has the pad effectively split in half with a deep groove running through it, the other is whole.

Can anyone help tell me which is front and which rear?

I believe the split is to allow the hot air/gases and dust escape from between the pad and disc (In the same way that you can get cross drilled or grooved discs).
I can't see it matters which ones go where as long as you are consistent front & back.

Thanks. I don't understand why they sell 2 different types if they are the same size. That said, on closer inspection I found one pad is thicker than the other.

I've looked into this some more. On PET, the parts numbers are the same, so why do they sell 2 different types for front & rear. Euro car parts have the rears for £24 and the fronts £11. Different compunds?

If the part numbers are the same then the pads & therefore factory compounds will be the same.
Euro Car Parts may just have multiple suppliers & not realise the pads are the same front & rear.