What's the difference between PTX and CUBIN w.r.t. the NVCC compiler?

I have CUDA 4.0 installed, and a device with Compute Capability 2.0 (a GTX 460 card).

What is the difference between the 'cubin' and the 'ptx' file?

I think the cubin is a native code for the gpu so this is micro-architecture specific, and the ptx is an intermediate language that run on Fermi devices (e.g. Geforce GTX 460) via JIT compilation. When I compile a .cu source file, I can choose between the ptx or cubin target. If I want the cubin file, I choose the code=sm_20. But if I want a ptx file I use the code=compute_20.

Is it correct?