Am2 and 4 ram modules

SoulStar · Aug 25, 2009

I recently found out that s939 motherboards underclock the ram with 4 modules instead of two. A64info program fixed that quickly (thanks forumites!).

I'm looking to upgrade and is there a difference between 2 and 4 modules on an AM2 motherboard?? Makes a difference between starting off with 2x1gig or 2x2gig DDR2.

Neuromancer · Aug 25, 2009

All AMD rigs downclock the ram to 800MHz when running 4 dimms I beleive.

I read something about the 4 way bank interleaving being really good though and it actually performs better with 4 dimms in a clock for clock comparison. No verification on this though.

Niku-Sama · Aug 25, 2009

i never had any problems with down clocking, this is some strange stuff

GrimX9 · Aug 25, 2009

Some mobos do this, they call it "AMD CPU limitation". IMHO its not a big deal depending on the original speed of the ram (1066).

Go for 2x2 sticks, makes it easier to overclock and you can run them at their rated speed (assuming 1066).

ekoh · Aug 25, 2009

Neur0mancer said:
All AMD rigs downclock the ram to 800MHz when running 4 dimms I beleive.

I read something about the 4 way bank interleaving being really good though and it actually performs better with 4 dimms in a clock for clock comparison. No verification on this though.

does this apply when running 4x2gb of ddr2 1066 sticks for 8 gig? reason i ask is because i saw this

Gigabyte MA790FX-DS5, And 1066mhz
Reviewed By: KENNETH64 on 2/20/2008 Tech Level: somewhat high - Ownership: 1 day to 1 week
This user purchased this item from Newegg
Pros: Bought 2 sets for 8GB, FOR GIGABYTE MA790FX-DS5, CPU=Phenom 9600 Black Edition. I am able to run all 8GB at 1066MHZ, O.S=VISTA ULTIMATE_X64. EVEREST ULTIMATE shows, mem timings as 5-7-7-20, 2T And memclock at 536MHZ.
Cons: NONE

Malakai · Aug 26, 2009

On intel and amd rigs, having 4 sticks of ram in there instead of 2 will cause the ram to not be able to run as fast. IE, 4 sticks of dual channel ddr2-1066 or ddr3-xxxx will not run at full speed at rated voltage the way it would with only 2.

CharlieCS · Aug 26, 2009

Malakai said:
On intel and amd rigs, having 4 sticks of ram in there instead of 2 will cause the ram to not be able to run as fast. IE, 4 sticks of dual channel ddr2-1066 or ddr3-xxxx will not run at full speed at rated voltage the way it would with only 2.

Pretty much sums it up , having both dimms filed loads the memory controller more heavily , and its not officially supported but alot of people are able to make it work.

Neuromancer · Aug 27, 2009

ekoh said:
does this apply when running 4x2gb of ddr2 1066 sticks for 8 gig? reason i ask is because i saw this

Gigabyte MA790FX-DS5, And 1066mhz
Reviewed By: KENNETH64 on 2/20/2008 Tech Level: somewhat high - Ownership: 1 day to 1 week
This user purchased this item from Newegg
Pros: Bought 2 sets for 8GB, FOR GIGABYTE MA790FX-DS5, CPU=Phenom 9600 Black Edition. I am able to run all 8GB at 1066MHZ, O.S=VISTA ULTIMATE_X64. EVEREST ULTIMATE shows, mem timings as 5-7-7-20, 2T And memclock at 536MHZ.
Cons: NONE

It does not mean you can not run the ram at 1066M HZ it just means the 1066 Mem Divider dissappears. (Or Maybe it doesnt, just defaults to 800?)

Most likely you default to 800 MHz than use the HTREF to clock it back up to 1066. 250 ish will put you right there

QuietIce · Aug 27, 2009

Neur0mancer said:
It does not mean you can not run the ram at 1066M HZ it just means the 1066 Mem Divider dissappears. (Or Maybe it doesnt, just defaults to 800?)

Most likely you default to 800 MHz than use the HTREF to clock it back up to 1066. 250 ish will put you right there

Come on! Anybody ought to be able to just set the CPU to 18x, vCore to 1.35v, NB to 11X, and have their machine run stable forever! You don't really expect them to use the clock do you?!?

I think in most cases it just defaults to 800 with 1066 still being an option. Don't know for sure, though. Like you I always use 800 and push the clock.

I also spring for bigger dual-stick kits if I want more RAM instead of having four sticks. I've tried four and it always reduces the OC. Even when running medium-sized CAD files the increased RAM doesn't make up for a slower CPU. It wouldn't surprise me if a good SSD would be better than more RAM if one really needed over 4Gb ...

crunchie · Oct 14, 2009

Just added two more RAM modules to make it 8Gb on my rig. Booted up fine and running at rated speed of 1066.
I never even went into the bios.
Processor running at 18x for a cpu speed of 3600.

Dapman02 · Oct 15, 2009

GrimX9 said:
Some mobos do this, they call it "AMD CPU limitation". IMHO its not a big deal depending on the original speed of the ram (1066).

Go for 2x2 sticks, makes it easier to overclock and you can run them at their rated speed (assuming 1066).

It also is easier on the Cpu's memory controller.

Malakai · Oct 15, 2009

On Core2* and AM2/+/3 mobo's, its the same. When you use 4 sticks instead of just 2, it puts a lot more load on the memory controller, and you will not (or usually not) be able to run them as fast as with just 2 sticks.

For instance, most of the time, 4 sticks of ddr2-1066 will only run at 800-900mhz, whereas just 2 of them will do 1066+ easily.

Its why my ram is only running at 800mhz. Cas4 works fine though. -266mhz but also slightly lower latency. IMO 8gb@800 >> 4gb@1066.

This goes for ddr3 as well. Same for i7 boards, 6 sticks will usually not run as fast as just 3 would!

So its not amd or intels fault, more just a shortcoming on current gen memory controllers.

Am2 and 4 ram modules

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