How does Triple Channel memory differ from Single or Dual?

Question

I'm trying to understand the PHYSICAL difference on the motherboard when it comes to single, dual, triple and quad channel memory.

I have a mobo that has 4 black memory slots, each one contains 4GB of RAM, a total of 16GB.

Since I have a 1155 socket I know I am limited to dual channel only.

But what about a 2011 socket? It supports quad channel memory but I do not understand how that would look on the motherboard, physically. I've seen many dual channel slots and there are only 2 colors.

Would triple or quad channels have only 2 color variants also or would there be more colors?

Answer 1

Would triple or quad channels have only 2 color variants or would there be more colors?

Not more colours, but a larger set of sockets in the same colour. E.g. a X58 based board (triple channel) would typically give you 6 sockets. 3 coloured blue and 3 coloured white.

• The X58/i920 has three memory controllers which can be used simultaneously.
  (aka triple channel).
• Memory controller #1 is connected to DIMM sockets A1 and 1B.
• Memory controller #2 is connected to DIMM sockets A2 and 2B.
• Memory controller #3 is connected to DIMM sockets A3 and 3B.

Since a typical consumer setup has a memory controller which can handle up to 2 dimm sockets^* this translates to 3x2 memory banks. You want to use all memory controllers at the same time, so you put one DIMM on each memory controller. This set has the same colour.

The typical setup can handle two DIMMS per memory controller. So you get a second set of colours.

In a consumer quad channel setup you would expect two sets of four. So two colours and 8 DIMM sockets.

In a server setup you will find more sockets per memory channel. E.g. my home server (A Dell R300) has 6 DIMM sockets. It is dual channel. So I got 3 sets of 3. Which is logically quite different from the two sets of three in my home desktop.

Based on this you can easily extrapolate for other configurations.

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^*Or rather up to 4 ranks. One regular consumer DIMM counts for 2 ranks, so that translates to 2 DIMMs. In server based boards this is often different, but that comes at the cost of speed.

Answer 2

The motherboard determines if you can use dual, triple or quad channel memory. This web site has a good explanation of the different types of memory.

In short, dual channel memory use twice the data lines as single channel memory. Triple channel memory uses 3 times the data lines as single channel memory. Quad channel memory uses 4 times the data lines as single channel memory.

The memory controller is faster than the memory access, so it overlaps the flow of data to increase speed.

Answer 3

The slot colors on a motherboard are arbitrary and non-standard. I recommend looking at the motherboard manual or PCB silk screen on the motherboard to understand which slots (or sockets) belong to which channel. Do not confuse a slot with a channel. Each channel will support one more more slots. Nomenclature for this is "DPC" or "DIMMS per channel"

A MOBILE CPU may support only one DPC.
A DESKTOP CPU product will generally support 2DPC
A HEDT (high-end desktop) / Workstation may support 3DPC
A SERVER product may support 4DPC or more.

Each channel represents an independent DDR memory bus. Since only one RANK/DIMM can communicate on a channel at once, there is an advantage to having more independent channels.

Single channel = 64-bit  memory interface
Dual channel   = 128-bit memory interface
Triple channel = 192-bit memory interface

DDR-1600 = 1600MT/s. 
(1600 * 64) / 8 =  12,800 MB/sec. **
(1600 * 128) / 8 = 25,600 MB/sec. **
(1600 * 192) / 8 = 38,400 MB/sec. **
** Theoretical maximum bus speed.  Unlikely to achieve.

The system will "interleave" or "stripe" (think raid-0) the data across as many channels as the system support.

Also, as you increase you channels, you increase your bank resources and thus you're able to simultaneously access more banks (rows) at a time. This allows the memory controller to pipeline data more efficiently.