Does Linux's NUMA architecture shares main memory as well?

I am reading about NUMA (Non-uniform memory access) architecture. It looks like this is the hardware architecture that on the multiprocessor system, each core accesses their internal local memory is faster than the remote memory. The thing I don't know is: looks like the main memory (RAM) is also divided between nodes. That makes me confused because I think all the nodes (which are stayed inside the same CPU) will have the same access speed to the main memory. So why does Linux divide the main memory for each node?