Dual Channels RAM Slots

[chrisling]

May I get clearer about motherborad which has dual channel of RAM? Let's say the dual channel RAM slot can support DDR533 and DDR400. Is that mean I can put DDR 533 and DDR 400 all mixed up to 4 slots? Or all DDR 400 up to 4 slots? Or only can put one type of DDR up to 2 slots as usual? Really quite blur about this... :(

[ski]

Typically, if there are 2 dual channel slots, then identical RAM modules must be installed, and if there are 4 slots then install 4 identical modules.

[chrisling]

May I know what's identical RAM modules? Is it something like virtual RAM?

[jlreich]

As ski indicated you must install ram in pairs to enable dual channel ram. Either 2 or 4 sticks.

Identical means the same speed, density and size in MB/GB's.

Note that Dual Channel is a function of the chipset and not anything at all to do with the ram itself.

The "Dual Channel Kits" that ram is often sold as are nothing more than a matched pair of sticks sold together to insure dual channel compatibility.

It is best to buy ram in pairs to insure compatibility, but not absolutely necessary. You can sometimes even pair up sticks from different manufacturers and it will run in dual channel mode just fine. It all depends on how picky a particular chipset is. But the two sticks must always be the same size and speed or it will not run in dual channel mode but default back to single channel mode.

[chrisling]

Is there any different with Single Channel and Dual Channel RAm slot? They seems to be the same from the aspect of the speed.

[jlreich]

No the ram slot is physically the same.

When in single channel mode data is stored on the first stick of ram until it is filled, then if necessary data is stored on the second stick and so on as needed.

When in dual channel mode two sticks are filled with data at the same time. Doubling the bandwidth, well theoretically doubled but not quite that good of a boost. For instance if you have DDR400, it would now be effectively DDR800 (theoretically). Hence the increase in performance. Like I said the performance increase does not turn out to be 100% but still ends up being a very good boost none the less. Very much like Raid 0 if you know anything about it.

Point is it has nothing to do with the ram slot or the ram itself, but rather a function of the chipset and the memory controller on the CPU to some extent.

[chrisling]

Thank you very much. It's very clear and I had learned it well. Thanks. :)