dual channel means 4gb + 4gb so you occupy port 1 and 3 or 2 and 4 out of 1 2 3 4 ram slots
This is just completely wrong.
Dual channel means DIMM 1 and 3 OR 2 and 4 OR 1,2,3, and 4 are occupied at the same time. Dual channel also has nothing at all to do with capacity. 2 x 1GB sticks run in dual channel as well as 2 x 4GB sticks do.
You can also mix capacity as long as they are matched. So 2 x 1GB and 2 x 4GB sticks will run in dual channel mode as well as 4 x 4GB sticks will.
Dual channel also only provides a net of 4-5% over single channel. So 2 x 2GB sticks are about 5% faster than 1 x 4GB stick.
1x2gb + 1x2gb + 1x2gb + 1x2gb = 8gb
Yes that is dual channel.