streams cuda how can offeres concurent execution

streams cuda how can offeres concurent execution

in cuda documentation, it is mentionned that if we use 2 streams (stream0
and stream1) like this way: we copy data in stream0 then we launch the
first kernel in stream0 , then we recuperate data from the device in
stream0, and then the same operations are made in stream1, this way , like
mentioned in the book "CUDA by example 2010", doesn't offer the conccurent
execution, but in the "concurrent kernels sample" this method is used and
offeres the conccurent execution. So can you help me please to understand
the difference beteween the two examples? thanks a lot for your help.