AM3: am I right in thinking it has to be 1 ram pair for Dual Channel mode?

[Zak33]

Lo people

On an AM3 mobo, with a Phenom II AM3 fitted, amd I right in thinking that the built in memory controller of the AM3 cpu can only support 1 pair of DDR3 ram modules for Dual Ram mode?

I know the boards often COME with 4 slots for ram, but somewhere, I've read that you need to just use TWO sticks of ram to get the fastest speeds from the DDR3 and memory controller, or it reverts to lower bandwidth.

Did I imagine this or is it fact?

[CAT-THE-FIFTH]

AFAIK as long as you have 2 banks or 4 banks of memory you should be able to run in dual channel mode(I think).

[kalniel]

Lo people

On an AM3 mobo, with a Phenom II AM3 fitted, amd I right in thinking that the built in memory controller of the AM3 cpu can only support 1 pair of DDR3 ram modules for Dual Ram mode?

I know the boards often COME with 4 slots for ram, but somewhere, I've read that you need to just use TWO sticks of ram to get the fastest speeds from the DDR3 and memory controller, or it reverts to lower bandwidth.

Did I imagine this or is it fact?

Lower bandwidth, yes, but not for the reasons you're thinking. Dual channel works for any even number of sticks, so 2 or 4 for eg.

However when you have 4 banks populated it's more work for the memory controller, which in most cases means you need to either run a little slower, or more usually drop to a slightly more latent command rate or timing. However this won't make a difference in any real world scenarios.

[scaryjim]

The original AM3 Phenom IIs weren't rated to run 4 sticks of memory @ DDR3-1333, so if you put 4 sticks of 1333MHz RAM in your mobo it'd automatically run them at 1066 instead (I believe the early S939 CPUs did something similar?).

I believe that the latest stepping (C3?) removed this restriction though, and AFAIK a lot of motherboards supporting overclocking the onboard memory controller to in excess of 1600MHz, so it shouldn't be a problem...!

[jim]

Same with Intel as well, their chipsets don't like 4 slots of RAM. My machine refused to POST, even with the CPU at stock, with all four slots populated.

[Biscuit]

i used to do it with my IP35-E and i swear that used to say 'dual channel mode' during boot up

[Zak33]

The original AM3 Phenom IIs weren't rated to run 4 sticks of memory @ DDR3-1333, so if you put 4 sticks of 1333MHz RAM in your mobo it'd automatically run them at 1066 instead (I believe the early S939 CPUs did something similar?).

I believe that the latest stepping (C3?) removed this restriction though, and AFAIK a lot of motherboards supporting overclocking the onboard memory controller to in excess of 1600MHz, so it shouldn't be a problem...!

that sounds about right... it's as close to what I remember as my old befuddled brain will allow

[ehhhhhhh]

it was the same with am2+ cpus as well, with 4 dimms it works at DDR2 800mhz or below. For a few days I did not have a clue why I got BSODs and mem test errors at 1066 (which seemed to be the correct setting).