I am using 512 MB Dual Channel RAM (2x256). My mobo has 4 dimms. If I want to upgrade (let say, to 1 GB), do I have to buy exactly the same 2 more 256MB sticks? Is the dual channel available if all 4 dimms are used?
Dual channel output from your DIMM's requires full bandwidth from the DIMM slots. On a 4xDIMM slot motherboard DIMM1/2 will most likely be on the same bandwidth and DIMM 3/4 will be on a different bandwidth (I don't know the exact terminology).
To enable Dual on my Asus K7N8X I hae 3 DIMM slots and Dual Channel mode will not work if I have memory modules in DIMM1 and DIMM2 - most motherboards colour the DIMM's different to show this.
