I'm not a computer scientist, but can someone explain to me how this can be a computer without all the other bits you normally associate with it other than the

I'm not a computer scientist, but can someone explain to me how this can be a computer without all the other bits you normally associate with it other than the CPU. I.e. a chip for interfaces, the mmu/fpu (I don't understand how you can get the cpu to cover this role?). I can see it doesn't have/need sound/gpu. Just would have thought more would be needed!