What's a difference between Cuda Core (Nvidia) and Stream Core (ATI)?

In ATI Radeon HD 5870 have 20 Compute Units, and inside of each compute unit have 16 Stream Cores, thus totaling 320 Stream Cores.

Already in Nvidia GEFORCE 560 your specifications said that have 336 Cuda Cores and when i run a application and get the number of compute units, it's returned 7.

If Cuda Core is the same of Stream core, then each compute unit have 48 cuda cores in Geforce 560?