Dual Channel RAM questions

Yeah when you "misplace" the RAM the performance is slower so you gotta test it around while it's on and when you misplace it (for example, a 512 RAM) becomes 334 for example so doing some switching around is good if you want to know why it loses performance...

Read the documentation about the motherboard. Some makers require that all 4 memory banks be the same to keep dual channel mode enabled, others will disable the dual channel on the memory that is mis-matched, and yet others will only enable dual channel mode on 2 positions and nothing else. The true answer is read your motherboard docs (or look them up online).

Here is one article i found, it's quite old, but it should answer some of your questions, and there's some benchmarking too.

http://www.devhardware.com/c/a/Memory/Dual-Channel/

Extracted from ASUS M2V User's Guide(My MOBO):

"For Dual-Channel configuration you may:
Install identical DIMMs in all four sockets
or
Install identical DIMM pair in DIMM_A1 and DIMM_B1(yellow sockets)"

So by that i guess that if you install a identical pair in DIMM_A1 and DIMM_B1 and also install another pair of DIMMs of the same latency and speed of the first pair but bigger size in DIMM_A2 and DIMM_B2 you lose dual-channel.

http://www.msi.com.tw/program/products/mainboard/mbd/pro_mbd_detail.php?UID=608 just in case anyone wanted to know

t0rek said:

1. How much performance is lost without using dual channel? if you guys like to, you might re-arrange your memory in your mobo slots and benchmark a little. I don't see any benchmarks of that around.

2. I know that if you use only 2 memory dimms one should be place in slot 1 and the other one in slot 3 and they have to be exactly the same (clock, latencies). My question is if you use 4 dimms, and they have the same clock speed and latencies, however 1 and 3 are bigger than 2 and 4 (see the pic below). Would you lose dual channel?

Click to expand...

To my knowledge, Dual Channel is just that - Dual Channel. That means two memories work together. Preferably they should be exactly the same, but this might vary from motherboard to motherboard.
The placement of the modules, as already explained, is up to the motherboard manufacturer and different companies do differently. So read the manual.
Now, if you have two 1 GB sticks and two 256mb sticks, it should work if you team up the 1Gb and the 256mb separately. There is no quadruple-channel (meaning there is no technology to bind four memories together; only two).
Dual Channel doubles the memory transfer rate (somehow ), so when not using it, your transfer rates is cut in half. Does this have an impact? Yes and no. A certain processor requires a specific amount of bandwidth from the memory to work Dual Channel, two sticks would give TWICE the bandwidth they would if not Dual Channel. If you have a higher bandwidth than required, you receive no benefits. If you have too low, however, your performance suffers. So if you have enough RAM, Dual Channel is useless.

This is what I have gathered from Tech Sites and assimilated. Hope that helps.

Dual channel ram controllers works, as doom mentioned, by doubling the bandwidth, it does this by taking two sticks of ram that lets say have a 64bit wide data bus each(that is they can transfer 64 bits, or 8 bytes at a time), if you pair them together and split off the first 4 bits of each byte to the first stick, and the last 4 bits to the second, then together they can transfer not 8 bytes, but 16 bytes at a time.

You may be wondering how a 64bit processor can make use of 128bits of a data... Of course, now is about when you should be realizing that your cpu runs at a much higher clockspeed Additionally, you should make sure your ram is clocked at a divider of a whole number, ie: if your CPU is 1.8GHz, you should run your ram at DDR 333, not DDR 400, as 333 goes into 18000 5 times where as 400 goes into 18000 4.5 times, which can cause increased latency and more wasted cpu cycles