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GA-MA785GM-US2H and ddr2 1066 memory

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August 14, 2009 12:36:35 PM

Oh-wiser-than-me-tech-type-folks,

Working on my first build and I think I made a little mistake by not researching my motherboard choice fully before ordering.

According to the Gigabyte site on the memory supported page for my motherboard it says "Note: Due to AMD AM3/ AM2+ CPU limitation, DDR2 1066 or above speed is only supported by 1 dimm per channel."

I got 8gbs (4X2GB) 1066 RAM. Since I got an AM3 Phenom II X4 processor am I understanding right that only 1 DIMM per channel will work with 1066 or higher RAM?

If so then I can either put all 4 2GB sticks on and it will run at slower speed (800?) or just put 2 sticks on (one per channel, which should be the 1st and 2nd DIMMS) and it should run at 1066 speed?

Am I understanding this right? If so would 8gbs running at 800 be slower than 4gbs at 1066? I am using this for gaming and I know that 8gb was overkill and my system building buddy has agreed to take the other 2 2gb sticks so I don't have to pay a restocking fee to new egg.

The thing that seems fishy from the Gigabyte documentation is that they indicate that only AM3/AM2+ has this limitation. Since the board supports AM2 also then the oldest cpu would allow 2 DIMMS per channel at 1066 or above but the newer/newest cpus would not? I am hoping this is an error in documentation or that I am reading/understanding it wrong!

Thanks very much for any advice on my rookie mistake. Have a great weekend!

- Jerry
a b V Motherboard
August 19, 2009 4:36:35 AM

Jerry,

I'm unfortunately not a great tech guru anymore, time has passed me a bit. (Should have seen me in the 80s and 90s!)

However, I'll start by saying that 8GBs of slower RAM vs 4GBs of faster RAM will always give you a speed benefit - and I'm assuming that you're not running Win XP. But of course, it's nicer to pay for 800 rather than 1066 if you're getting 800 speed!

I'm looking at buying the same board or my preference, the full ATX version the GA-MA785G-UD3H. And I get the same reading from the MB memory chart that you're getting. But it would be nice to know what "v" means in the chart. If "v" means "full banks" then our reading of it is right.

Since you actually have the RAM in hand, here's what I suggest. First, see what the BIOS and POST are saying about the memory when you have all 4 banks filled.

Next use some easy-to-use software such as SiSoftware Sandra (avail free at download.com) and examine the mainboard under hardware. Look at the configurations of the memory and compare the readouts using 4 banks vs 2 banks. The type of memory shown may differ - but the timing/latency of 2 vs 4 should vary for sure if the 1066 RAM is running at 800. Look up the latency values for the exact type of RAM you purchased, if it's not on the purchase website, try the manufacturer's site. In addition, the Voltage of the RAM may vary depending on the usage speed (not sure).

For example: Corsair's PC6400/800MHz DDRII has latency/timing of 5-5-5-18 but Corsair's PC8500/1066MHz is 5-5-5-15

Your brand may vary more than my example.

And, since I haven't placed my order yet, I'd be interested in knowing. I'm looking at the choice of 2 2GB banks of 1066 or 800 - but the idea for me is to get the most out of my Win XP with 4GBs then expand with more of the same memory later when I upgrade OS. But like you, there's no point in buying the 1066 now if when I fill out the banks later I'll be limited to 800 speed.

So please let me know what you find out.
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a b V Motherboard
August 22, 2009 12:12:57 PM

It is not the board guys, it is a limitation of the AM2+ platform and the Phenom processors.
You have to go full AM3 board and processor, DDR3 memory to get around this.
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a c 177 V Motherboard
August 22, 2009 6:44:49 PM

This issue gets really interesting - I'm not positive, but I think GB is just playing CYA, as there seem to be no harware documents from AMD to support this limitation, but I think operation of multiple DIMMs per channel past 800 may depend upon the memory controller interface specification of the actual DIMM selected...

First, I couldn't find anything specific for the MOBO in question (all damned ads!), but I came across this, for another:
http://forums.guru3d.com/showthread.php?t=283918

Next, I dl'd a batch of AMD docs from here:
http://support.amd.com/us/psearch/Pages/psearch.aspx?ty...
Unfortunately, some of the more comprehensive docs date from 2004; here is a pub from '07, stating 800:
http://support.amd.com/us/kbarticles/Pages/DDR2-memory-...
Nowhere in the relevant RAM I/O specs on pages 12-27 of this doc:
http://support.amd.com/us/Processor_TechDocs/31119.pdf
is an upper limit, beyond signal slew rates, defined...
Another '07 doc says 400MHz RAM controller (DDR2-800), but it again is old:
http://support.amd.com/us/Processor_TechDocs/43042.pdf
This one, too, seems to say 800 limit (page 29 & 30), but it, again, is an '04 doc:
http://support.amd.com/us/Processor_TechDocs/31684.pdf
and this, again an '04, seems to say on page 12 that a channel can be four G wide:
http://support.amd.com/us/Processor_TechDocs/41322.pdf
Likewise, the actual HyperTransport Link Def doc:
http://www.hypertransport.org/docs/tech/HTC20051222-004...
nowhere defines an upper limit on any variety of link types, just defines relative standards and timings...

So, after reading roughly 350 pages of documentation, I can give you a solid, qualified "I don't know!!"
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September 12, 2009 5:47:10 PM


I have exactly the same situation; SiSoftware Sandra shows my 4 dims (2 dims per channel, 8GB total) as DDR2-800 (when they are in fact DDR2-1066 modules)

Have any of you guys been able to find whether it's a limitation on the board or the processor itself?

Thanks,



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a b V Motherboard
September 12, 2009 5:57:41 PM

jogar - you're in the position to make a test and verify that this is indeed true. Take out two of the modules - without changing BIOS settings - and see if they then come up as 1066 and show as such in Si Sandra.

Now, if the two modules don't show as 1066 - get them working!
Verify the correct voltage required by the mfgr is what the board is pushing. Most inexpensive 1066 RAM wants 2.1-2.2Vs and base voltage on this board is 1.8V

Give us the specs, the maker and model # and the info from the SPD too.

I'm assuming you have 4 identical modules?

Thanks and hope you can test this.

I did buy this board myself and have 2 2GB 1066 modules using 1.8V.

(Also, my board "says" it's delivering 1.8V to RAM but Si and HWMonitor saya that in Auto voltage mode, it's actually delivering 2.05V. I'd be interested in what's showing on yours. If I manually set RAM V to 1.9, it sends exactly that. It's just the Auto V on both RAM and CPU that pushes more.)
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September 15, 2009 7:19:39 PM

Thanks very much for the thorough replies and more-than-i-could-ask-for amount of research everyone! The truth is I just left the BIOS settings at 1066 for the RAM and dropped the other 4gbs in a couple weeks ago. The system took anything I threw at it with only 4gbs and with 8 I still can't begin to run any one or multiple programs that it can't handle. I was excited the last bunch of months to learn about pc parts and build this new pc... but now I am excited to go back to playing games. I am not going to have a chance to run any programs to measure what speed the RAM is running at or even mess with the settings... I wanted to build a pc for gaming that would run anything and I did. I have had no problems with this motherboard and the RAM so I would certainly recommend. Good luck to everyone with their builds and upgrades. Thanks again for the feedback!! :D 
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a b V Motherboard
September 15, 2009 8:00:39 PM

Bottom line, if you want to run at 1066Mhz then don't buy more than 4Gb's (2x2Gb), if you buy 2 sets of ram for a total of 8Gb's then buy 800Mhz and save the extra cash.... AMD CPU's cannot run 8Gb's @ 1066Mhz, it will auto default to 800Mhz no matter what....
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September 16, 2009 7:43:51 AM

Ah, That answers the technical question about the RAM speeds. But the quest posed by GHF was: is it better to run 4gb of DRAM at 1066 or 8gb at 800?? I think it wouild take some benchmarks to answer, like Sysmark or various game benchmarks.
For me, I'm running XP, so anthing over 4gb is wasted....
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a b V Motherboard
September 16, 2009 8:45:29 AM

Mongox said:
Jerry,
However, I'll start by saying that 8GBs of slower RAM vs 4GBs of faster RAM will always give you a speed benefit - and I'm assuming that you're not running Win XP. But of course, it's nicer to pay for 800 rather than 1066 if you're getting 800 speed!


I did answer that! From what I've read, it's just impossible for an OS not to enjoy more RAM - it'll always find something to do with it. Doesn't mean it's the best way to spend your money, but he didn't ask that!

Like you Pat, I got the MA785GM-US2H but didn't know about matching the voltage ability of the MB to the RAM requirements. I got OCZ 1066 RAM that wanted 2.2V but many boards including this one are limited to 1.8V - 2.1V. Even then the bright red text in the BIOS makes you fearful of it! I ended up RMA'ing the OCZ and got some Crucial with slower latency. Now OCZ is making the exact same RAM w/1.8V - likely in response to so many returns. The Eggy folks made things right by removing the restocking fee but turned me down on the option of replacing me yet again with the newer (and more expensive) OCZ modules.

So I'm running 1066 w/6 instead of 5, oh well. I did try to ask the right questions! And if either of us end up adding another pair of RAM to any AM2+/AM3 motherboard, it'll drop the speed to 800, it's the way the memory is addressed by the CPU.
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a b V Motherboard
September 16, 2009 3:27:25 PM

If you are running XP 32bit then 8Gb is a waste of money since the OS can only see 3.25Gb. Now, if you are going to upgrade soon to a 64bit OS then 8Gb of 800Mhz is superior to 4Gb of 1066Mhz regardless... remember that 1066Mhz is really 800Mhz modules that run at a higher speed, meaning a 64bit OS benefits off of more GB not Mhz... The more ram you have for a 64bit OS the better.... I will soon install Win 7 64 and will end up buying 2 more sticks of 800Mhz ram.....
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a b V Motherboard
September 16, 2009 4:29:25 PM

Oddly enough, NewEgg has now made the new low-voltage OCZ vanish from their website. They show the 2.2V model - OCZ2P10664GK. I thought I saw a review on this RAM by you OvrClkr - if so, it's gone now.

The 1.8V model - OCZ2P1066LV4GK - was there yesterday and I even submitted a review of it. And put it in my Cart to keep track of it while I negotiated with them about the re-stocking fee on my 2.2V order. Today my cart says "N82E16820227452 has been removed from shopping cart due to quantity limitation/insufficient stock."

Maybe they have too many of the 2.2V in stock and figure they won't sell - but companies don't stock much RAM so I dunno. Or they think it might give more ammo to those who get stuck with the 2.2 - more likely.
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a b V Motherboard
September 16, 2009 4:48:40 PM

Yea I saw that.... there were no reviews on that 1.8v RAM.... Who knows where you can get them now.... Would have been nice to at least test them out and see if there are trully stable at 1066Mhz.....
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a b V Motherboard
September 16, 2009 5:44:54 PM

Well, I'm happy with my Crucial/Microns - I didn't want to pay the $75 range for the CL 5 range RAM and was determined to get 1066! They're rated at 7 but I'm running at 6 and doing fine.

Once I get in my new fan/cooler I'm gonna try fooling around with OC - something I know little about. I've already got my 785's graphics speed 500 to 800. My question in the AMD OC forum is lingering w/o answers - wondering if a unlocked 550 draws 125W afterwards?

When I'm ready to OC, I'll post over there and might send you a pm to ask you to respond.
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