Some of the boards run dual data memory that would is 2 sticks. These boards have from 2 slots to 4 slots for memory.
Some of the boards run triple data memory and that is 3 sticks. Most of theses boards have have 6 slots for memory.
Some of the boards run quad data memory and that is 4 sticks. These boards have from 4 slots to 8 slots for memory.
On your board you run dual data memory so that would be 2 sticks. You board has 4 slots for memory. Yes you can run 1, 2, 3, or 4 sticks of memory.
For the best performance you should run 2 sticks or 4 sticks and not 3 sticks. Always keep you memory in pairs and plus all the same too.
Yes the 3 sticks will run but you will better off running 2 or 4 sticks of memory.
So if you want to have 4 gbs of memory you should buy it as 2 sticks of memory being 2 gbs ea = 4 gbs.
If you want 8 gbs you can buy 2 sticks 4 gbs ea = 8 gbs or 4 sticks at 2 gbs ea = 8 gbs.
If you want 16 gbs you can buy 2 sticks 8 gbs ea = 16 gbs or 4 sticks at 4 gbs ea = 16 gbs.