Solved How does Dual-Channel RAM architecture work?

[DextrousDave]

Hi All

I would like to know the requirements of dual channel architecture RAM:

Here is my understanding:


- Dual-Channel Architecture uses Banks consisting of pairs of RAM slots (2 slots per bank)
- Both Slots must contain a RAM DIMM (Stick) - eg. You cannot put a single RAM DIMM into a dual channel bank, both slots
must be filled...
- RAM DIMMs in a bank(matching pair) can have different speeds BUT the slower RAM speed will be chosen...
- RAM DIMMs in a bank(matching pair) can have different sizes/capacities(eg. 1x2GB and 1x1GB)
- RAM DIMMs in a bank(matching pair) MUST be of the same type - eg. DDR, DDR2, DDR3 etc

Am I correct on all my 'assumptions'?

Thank you

 

[DeaconFrost]

Some of your assumptions are true regardless of what type of chipset they are going into. But I think I can clarify.

A dual channel refers to two slots working as a bank. So in those two slots, you will want to have matching pairs (as you said). Matching pairs means the same memory...same type, brand, speed, capacity, etc. If you mix memory, you run the risk of it not functioning properly. Anytime you mix memory, you run that risk of instability.

Considering the fact it's been 8-10 years since memory has been available in pairs or kits, there's no reason anymore NOT to use matching pairs. You can mismatch across banks, though. For example, I have 4 memory sticks. They are identical in ever way, except I have 2x4 and then 2x2 for a total of 12 GB. All memory is the same brand, speed, timing, etc.

 

[DextrousDave]

Ok cool thank you. So what I understand is that you can mismatch inside a single bank but it is not advised(depending on the motherboard). Also, in dual channel you have to fill both slots right? Filling one slot won't work?

 

[GeneO]

It should work, but at least the single DIMM will run in single channel mode, so it will be slower.

 

[kbrady1979]

For best performance, assuming your motherboard has 4 DIMM slots, you need 2 or 4 sticks of the exact same RAM. Same frequency, timing, and capacity. Symmetry plays a big part in RAM performance.

Example: My old rig came with 3GB of RAM. 2x1GB sticks in one channel, and 2x512MB sticks in the other channel. Exact same frequency. It scored a 6.0 in WEI. I took that out and installed 4x1GB of the same RAM and it went from a 6.0 to a 7.1 in WEI! I reran the assessment because I thought it was a fluke. Sure enough, it had improved the performance that much, and going from 3-4gb in capacity didn't account for the difference.......it was everything being symmetrical. I would either get a 2-stick kit or a 4-stick kit that was matched and rock on.

Here is a picture of a MSI motherboard, focusing on the DIMM slots.

Notice the different colors, blue and black. If you had two sticks of RAM you would install them in either the blue slots OR the black slots. That is how the channels are seperated. Refer to your motherboard manual or website to see which channel is which......if you are only using 2 sticks. For example, in my Asus Sabertooth mobo, if installing 2 sticks only, I would use the 2nd/4th slots, although if you are using 4 sticks, you would obviously populate all 4.

Hope this helped

 

[DeaconFrost]

Ok cool thank you. So what I understand is that you can mismatch inside a single bank but it is not advised(depending on the motherboard). Also, in dual channel you have to fill both slots right? Filling one slot won't work?

I wouldn't even bother trying to mismatch, especially given how cheap memory is now. In the end, it isn't worth a huge amount of effort. Dual channel memory configurations are faster than single channel, but not wice as fast. You likely wouldn't see a difference between the two until you ran some memory benchmark utility. Many new laptops come with one slot only, or only one slot filled.

 

[DextrousDave]

Thanks everyone, appreciate your answers!

 

[Joan Archer]

Some laptops also come with mismatched, our Toshiba has 6GB of RAM and as you can't get a 3GB stick it's made up of a 4GB stick and a 2GB stick, it only has 2 slots so can't be running dual channel as each slot has a different size in it.

I'm no expert but those are my thoughts on the subject.

 

[longbikez]

an interesting piece of history

I'm running a epox board that was built with 3 slots. 2 in a pair on one chan. and a single for the other chan. In WinXP and in Linux I can fully populate all three slots with their max value which is 1GB per slot.

But with Win7 I can only populate the two in a pair for single channel or one in each of the channels for a max of 2 GB in any of the allowed combinations.

If I put in 3GB of ram I get BSOD and no boot up 0x0000000A.
The ram is all new and has all passed every test I can throw at it.

A local IT guy says that 7 is prejudiced against non-paired ram and there is no way to fix this. He suggested I try a 10 disk but I told him that my AMD XP cpu is too old for anything newer than 7.

So anyone any ideas??? or am I truly been abandoned by MS.
IMHO only a merchant who is a fool turns his back on a paying customer, but then MS has been playing that for quite a while.

Lucky for me there is Linux Mint so I can still surf the net. I use my old XP drive for running programs that are incompatible with Linux.
As it is, my 7 drive just sits there b/c who wants to pull a stick out just to run it.

Thanks for any ideas.
Dave
no money for anything newer.

 

[AddRAM]

3 memory slots, no sata ports, AGP ? how old is that board ?

 

[longbikez]

very, and also very famous, "the over-clocker’s dream"
It ain't broke.