Official GIGABYTE Forum

VERY IMPORTANT INFORMATION REGARDING AMD AM3 CPU's and RAM SPEEDS

absic

  • *
  • 5714
  • 516
  • Never give up; Never surrender!
VERY IMPORTANT INFORMATION REGARDING AMD AM3 CPU's and RAM SPEEDS


There have been a lot of instances where members have been unable to obtain the stated speed of their RAM especially if it is faster than 1333 Mhz. In an effort to address these problems I have undertaken a lot of research and testing to come up with some honest answers for those of you experiencing such issues.

The following comments are not those of Gigabyte or AMD but are my own, based on the research I have undertaken and the questions I have posed to both parties in an order to gain a greater understanding of the subject and are, to the best of my knowledge, correct at the time of posting.

First off you should understand that this is not due to a problem with Gigabyte Motherboards or the BIOS. Other manufacturers boards also have the same problems.

It is due to the Memory Controller on the AM3 CPU's which, by design, are set for 1333 Mhz memory modules or slower. That doesn't mean that you can't run 1600 Mhz RAM or, even if you do, that you are entering the realms of overclocking (although it can seem like it) but, it does mean that you need to understand the inherent problems of running your RAM above 1333 Mhz. on these Processors.

This problem is more noticable if you are trying to run with all 4 memory slots filled on the motherboard but can also apply if you are only using 2 sticks of RAM.


Having actually talked to an AMD Technical Guru to establish their views on this subject, I can now state, with confidence that:

You are better off not trying to run your RAM above 1333 Mhz. when using an AM3 Phenom or Athlon CPU.
If you do so, you run the risk of system instability and even damaging the Memory Controller on the CPU. If, like me, you have invested in 1600 Mhz RAM, you will actually benefit from running your RAM at 1333 Mhz and tightening the timings. You also gain better performance by slightly overclocking your CPU. If, however, you do overclock your CPU, it is stongly recommended that you purchase a good quality 3rd party CPU heatsink to aid CPU cooling and also remember that officially, neither Gigabyte or AMD support overclocking of their products.

If you wish to run RAM above 1333 Mhz. and your RAM is rated at a higher speed, you are not overclocking your system. However, AMD recommend that you only use memory that appears on the QVL as this has been tested for compatability at higher speeds. If you are unsure about the compatability of the RAM you have bought the safest option is to run it at 1333 Mhz to avoid damaging the Memory Controller. If you are looking to buy RAM that is faster than 1333 Mhz. and it doesn't appear on the QVL be prepared to downclock the modules to gain system stability. There are no guarantees that the RAM will run as stated and you could possibly damage the CPU's Memory Controller.

THIS IS VERY IMPORTANT:
If you do manage to get your RAM running over 1333 Mhz., your system can appear to be fine and might even pass Memtest and other benchmarking utilities successfully. However, AMD have discovered that, in certain scenarios, the system may fall over after a period of use, depending on system usage and if you are stressing the CPU. This normally indicates a problem with the Memory Controller and you may need to replace your CPU if this happens.

Excessively increasing voltages to the RAM and/or CPU in an effort to improve system stability could cause the Memory Controller to fail.


AMD recommend running RAM in Unganged  mode.
From my own testing, RAM above 1333 Mhz can be extremely fussy if you insist on trying to run in Ganged Mode and will often return an Overclock warning at start-up and revert to 1333 Mhz., by default. In most modern mult-threaded applications there is actually no loss in performance when running in Unganged Mode and, in some instances, Unganged mode is actually superior.

Some of the Athlon CPU's have a memory speed rating of 1066 Mhz and will pull back RAM above this speed to the default setting. This is again to protect the CPU's Memory Controller and is not a fault with the Motherboard, BIOS or RAM.

The lack of easily available, clear and concise information regarding the AM3 CPU architecture and in particular the Memory Controller on these CPU's has led to a lot more problems than there really should be. It is understandable that AMD don't want to shout out too loudly that their AM3 CPU's do not handle the faster RAM speeds efficiently but it really hasn't been helped by the lack of information from all of the motherboard manufacturers regarding this subject as well.

I hope this helps those of you facing such issues and, if you are looking to invest in an AMD AM3 CPU, an understanding of what to expect and which memory speed to be looking for.


This ties in with another thread on the forum. Please check here for more information: http://forum.giga-byte.co.uk/index.php/topic,2379.0.html


A LITTLE CLARIFICATION REGARDING GANGED/UNGANGED MODES & SINGLE/DUAL CHANNEL CONFIGURATION.

Ganged Mode and Unganged Mode are not the same as Single Channel or Dual Channel configuration.
The Ganged/Unganged mode refers to how the RAM Modules actually talk to the Memory Controller(s) on the CPU.
Single or Dual channel configuration refers to how the RAM is installed in the memory slots on the motherboard. With one stick of RAM you are using single channel mode. With two sticks of RAM you can run in either Single or Dual Channel mode depending on how you fill the Memory Slots on the motherboard. If you use three or four sticks of RAM you will be running in Dual channel mode.

On Gigabyte's AMD Boards there are two channels, each of which address one of the two memory controllers on the AM3 CPU. Channel 0 normally equals the Memory slots on the motherboard identified as DDR3_1 & DDR3_3 whilst Channel 1 normally refers to DDR3_2 & DDR3_4.

If, for example you have two sticks of RAM and you put them into slots DDR3_1 & DDR3_2 you are running in Dual Channel Mode, each stick of RAM talks to its own Memory Controller. If you put the RAM into slots DDR3_1 & DDR3_3 you would be running in single channel mode, where both sticks of RAM are only talking to one of the Memory Controllers. (You would need to double check with your motherboard's own manual for correct Memory Slot Channel configuration)

Ganged Mode is where you utilize both Memory Controllers on the CPU as a single unit giving you a single 128 bit channel. (You may not be able to run RAM faster than 1333Mhz in this mode. I haven't been able to with either the X4 965 or the X6 1090T.)

Unganged Mode is where each of the Memory Controllers on the CPU work independently and equals 2X64 bit Channels. (I can run my RAM at 1600 Mhz only in this mode)


If you have any comments or questions regarding this article please post them here: http://forum.giga-byte.co.uk/index.php/topic,3061.0.html

Edited: 09/10/2010
« Last Edit: December 05, 2010, 06:32:03 pm by absic »
Remember, when all else fails a cup of tea and a good swear will often help! It won't solve the problem but it will make you feel better.

absic

  • *
  • 5714
  • 516
  • Never give up; Never surrender!
Re: VERY IMPORTANT INFORMATION REGARDING AMD AM3 CPU's and RAM SPEEDS
« Reply #1 on: August 10, 2010, 08:20:56 am »
Quote
The Phenom II only supports 1333MHz DDR3—at least, officially—with a single DIMM in each memory channel. With four DDR3 DIMMs, 1066MHz is the standard. Such limitations are nothing new, of course. Previous Phenoms have long supported 1066MHz DDR2 memory, but only with a single DIMM per channel.

The quote written above was taken from Techreport.com item published in February 2009. For the full article please check here: http://techreport.com/articles.x/16382
Remember, when all else fails a cup of tea and a good swear will often help! It won't solve the problem but it will make you feel better.

absic

  • *
  • 5714
  • 516
  • Never give up; Never surrender!
Re: VERY IMPORTANT INFORMATION REGARDING AMD AM3 CPU's and RAM SPEEDS
« Reply #2 on: November 08, 2011, 12:27:03 pm »
I thought it was about time to update this thread with a little more information.

The RAM speed issues DO NOT apply to the latest AM3+ Bulldozer FX CPU's which are rated to run RAM at up to 1866MHz

If you are running a Phenom ii X6 CPU with the E0 stepping you will usually be able to run your RAM at 1600MHz. The risk to the Memory controller is slightly less on these CPU's due to the different Stepping version.
Remember, when all else fails a cup of tea and a good swear will often help! It won't solve the problem but it will make you feel better.