DDR3 - mixing different sized pairs of RAM & dual channel configuration

efishta

Limp Gawd
Joined
Oct 12, 2004
Messages
184
Hi fellas,

got a question that I was doing a bit of research earlier on due to a deal I saw on Slickdeals for a $46 8GB DDR3 pair of RAM.

Currently I've got 4 x 2GB 1333 DDR3 sticks in the Gigabyte H55 1156 motherboard, paired with an OC'ed Core i3. It's all very groovy, works great in dual channel configuration, very stable etc.

Now, seeing as I want to partake of this deal, I'm wondering what would happen if I were to have 2 x 2GB & 2 x 4GB running in dual channel.

My motherboard manual doesn't tell me what would happen, but several Google searches later and I found a thread on Tom's HW quoting from an ASUS manual of a P55 chipset mobo saying:

"You may install varying memory sizes in Channel A and channel B. The system maps the total size of the lower-sized channel to dual-channel configuration. Any excess memory from the higher-sized channel is then mapped for single-channel operation."

The caviats being that I don't have an ASUS board, nor is it a P55 board (H55, although it should be similar enough), how do you read this?

Does it mean that I would be running at 4GB dual channel (total size of the lower-sized channel and 8GB single channel) or 8GB dual channel (total size of the lower-sized channel times two, since it's two different sets of RAM and it'll be using 2 x 2GB from each bank of memory, with a 4GB single channel)?

It's a bit of a pointless question since the difference between worrying about this at all or not is another $46 for another 8GB pair, but it's more curiosity if anything.

I don't have extra RAM to test this out with or I would post my finding here.
 

Wildace

Supreme [H]ardness
Joined
Jun 16, 2004
Messages
6,721
you would be running 8GB total, 2x2x2x2 which negates the reasoning for having the old stick to begin with since only 2 sticks will usually be mroe stable but since you dont have an overclocking board it prob wouldnt matter either way. but imo you might aswell use the new sticks and sell the old ones
 

efishta

Limp Gawd
Joined
Oct 12, 2004
Messages
184
So that would be 2x2GB & 2x2GB at dual channel, and the remainder, 4GB, at single channel then?
 

Wildace

Supreme [H]ardness
Joined
Jun 16, 2004
Messages
6,721
no the computer would ignore the other 4gb as if it did not exist.

which is why there would be no point to have the old sticks in the system.
 

plugwash

[H]ard|Gawd
Joined
Sep 17, 2010
Messages
1,547
Wildace's posts are BS modern motherboards can use all the ram pretty much regardless of what module configuration it is in.

Also you can get all your memory in dual channel with 2x4GB and 2x2GB as long as you put it in the correct slots.
 

Wildace

Supreme [H]ardness
Joined
Jun 16, 2004
Messages
6,721
are you sure? guess things have changed doesnt suprise me tho my bad :eek: ive always used same size ram stick to avoid such issues. seems odd to me that dual channel would work with mix matched sizes but if it works i wont argue it :)
 

defaultluser

[H]F Junkie
Joined
Jan 14, 2006
Messages
14,399
are you sure? guess things have changed doesnt suprise me tho my bad :eek: ive always used same size ram stick to avoid such issues. seems odd to me that dual channel would work with mix matched sizes but if it works i wont argue it :)

Absolutely. See here:

http://www.intel.com/support/motherboards/desktop/sb/cs-011965.htm

You can easily run 4x2 with 2x2 for 12GB total. You can also run 6GB (2x4) in Flex Mode dual-channel, and get NEARLY the same performance as matched sticks.

Memory controllers are REALLY flexible these days :D

H55 max memory is 16GB, so it will accept 4GB sticks.
 
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