Why do some DDR3 sets come in threes?

[dds14u]

For Example:
http://promotions.newegg.com/I...2fcorei7%2f620x130.jpg

Is it a marketing gimick?

Is there a performance benefit?

 

[Adam8281]

I believe DDR3 runs optimally in sets of 3, like DDR2 runs in sets of 2. So motherboards on the new Intel chipset have 2 banks of 3 RAM slots, instead of 2 banks of 3. For a picture, see this recent Anandtech article: http://www.anandtech.com/mb/showdoc.aspx?i=3459

 

[imported_michaelpatrick33]

Actually DDR3 has nothing to do with three channels in of itself. DDR3 kits of three are for the new Intel i7 Nehalem cpu with tri-channel integrated memory controller. DDR3 still runs in pairs on older Intel chipsets X48. DDR3 is just the next iteration of memory SDRAM-DDR-DDR2-DDR3 etc.

Edit: Runs in pairs X48 to keep the dual-channel configuration but can run in three slots or two or one if necessary but most boards come with four slots for dual-channel.

If you are purchasing or have the I7 then the matched three module kit is the way to go for maximum performance with Nehalem. If you have an older X48 board or equivalent then go with a paired memory kit (don't fill the third slot if you have a dual channel cpu) as this would drop you to single channel (and won't give you maximum performance though the extra ram may make up the difference depending on the application).

To answer, it is not a gimmick per se but a marketing strategy and having exactly the same memory modules can be a plus in a multi-dimm configuration.

 

[Concillian]

Intel's new processors "Core i7" have triple channel memory. Triple DIMM kits are for those processor / motherboard combos.

Reviews indicate that there is a bandwidth improvement from triple channel. However, just like the old single channel vs. dual channel debates when dual channel first burst onto the scene, triple channel is currently offering very small to no performance benefit over dual channel.

I believe Intel has eventual plans to release i7 chips with a dual channel socket for more mainstream applications.