[war59312]

What's needed for the dual-channel mode? At least, two memory modules, with one installed exactly into the DIMM0 slot which is arranged differently than DIMM1/2 or DIMM1, with the DIMM2/3 being provided as well. In case of wrong installation the second memory controller might not operate. The modules can be different (as well as their producers), but their speed characteristics should be the same, otherwise the system will operate at the speed of the slower one (for example, DDR266 in case of one DDR266 and one DDR400 modules). It's also possible to use three modules, but remember that the dual-channel access can be set only for the memory size equal to the double size of the first module (which is installed into the slot of the lowest number), and if the size of the first module does not exceed the sum of the sizes of the second and third modules. Obviously, there are two most optimal cases: equal memory modules inserted into the first and second slots, or three modules, with the first one being equal to the sum of the other two modules.

So not sure about four.

What mother board do you have?