Q&A for the topic VERY IMPORTANT INFORMATION REGARDING AMD AM3 CPU's & RAM....

[wanner]

I have an X4 945 processor which has locked multipliers .My memories are rated at 1600MHz.
What if I overclock the CPU by increasing the FSB. By doing this I will also increase the speed of the memory. Does this mean that I should underclock the memories in order to not exceed 1333MHz?

[absic]

Hi,

good question and one I had to double check with my own system before replying to.

If you set your RAM to 1333 Mhz (which I would strongly recommend you to do) when you increase the CPU Multiplier to overclock the CPU the RAM will stay at 1333 Mhz. I think this is because the Memory Controller is now part of the CPU, not part of the Motherboard Northbridge. The extra headroom that the 1600 Mhz RAM gives you when downclocked to 1333 Mhz gives you more room to manoeuvre with the overall increased speed of the CPU.

If you are going to overclock your CPU remember to make sure you have a good heatsink and be careful to monitor temperatures as they can get rather high. Also don't forget to take into account that AMD & Gigabyte do not officially support Overclocking and doing so can void your warranty.

Hope this helps.

UPDATE:
Just digging into this a little more I came across this thread at Overclockers. http://overclockers.com/forums/showthread.php?t=642099
Although the guy is using an X6 CPU if you look at the first picture you'll see he has got 4 Ghz with the RAM set at 1333 Mhz. The same would apply to all of the Phenom ii CPU's

[wanner]

Hi,

good question and one I had to double check with my own system before replying to.

If you set your RAM to 1333 Mhz (which I would strongly recommend you to do) when you increase the CPU Multiplier to overclock the CPU the RAM will stay at 1333 Mhz. I think this is because the Memory Controller is now part of the CPU, not part of the Motherboard Northbridge. The extra headroom that the 1600 Mhz RAM gives you when downclocked to 1333 Mhz gives you more room to manoeuvre with the overall increased speed of the CPU.

If you are going to overclock your CPU remember to make sure you have a good heatsink and be careful to monitor temperatures as they can get rather high. Also don't forget to take into account that AMD & Gigabyte do not officially support Overclocking and doing so can void your warranty.

Hope this helps.

UPDATE:
Just digging into this a little more I came across this thread at Overclockers. http://overclockers.com/forums/showthread.php?t=642099
Although the guy is using an X6 CPU if you look at the first picture you'll see he has got 4 Ghz with the RAM set at 1333 Mhz. The same would apply to all of the Phenom ii CPU's

From the pictures it looks as he has left the FSB@200MHz and increased the multiplier. If you change the HT Ref Clock you will increase the speed of the memory as well?

I tried increasing the HT Ref Clock from 200MHz to 220MHz and here are the results.



Before OC the memories ran at 666.7 * 2 = 1333.4 MHz
After the OC they ran at 733.4 * 2 = 1466.8 MHz

So it does indeed seem that the speed has changed?

Please correct me if Im wrong.

[absic]

Yes, if you increase the speed of the HT link then the RAM speed will increase. But as your RAM is rated at 1600 Mhz you are still below the threshold of 1600 Mhz that I was alluding to which is why I said to downclock to 1333 Mhz.

The only problem that I envisage with bumping up the HT Link is that the system could become unstable due to the limits of the Memory Controller and the increased speed of the RAM. Normally, increasing voltage could help with system instability but, I would be very wary of doing this.

If you leave everything at default and just increase the CPU multiplier you gain from the increased speed of the CPU without running too much of a risk of damaging the Memory Controller.

As they say: "You pays your money, you take your choice."

[wanner]

If you leave everything at default and just increase the CPU multiplier you gain from the increased speed of the CPU without running too much of a risk of damaging the Memory Controller.

Phenom II X4 945 has a locked multiplier which means it cant be increased over 15.

[absic]

Sorry, my bad and you are right.

but as I said earlier, even when you increase the HT Link your RAM is still running below 1600 Mhz and, as long as your system is stable, it shouldn't be too much of a problem.

The other option would be to drop the RAM to 1066 Mhz and see if you can gain more from the CPU as this should keep the RAM to nearer the 1333 Mhz and might be a safer choice.

[wanner]

Sorry, my bad and you are right.

but as I said earlier, even when you increase the HT Link your RAM is still running below 1600 Mhz and, as long as your system is stable, it shouldn't be too much of a problem.

The other option would be to drop the RAM to 1066 Mhz and see if you can gain more from the CPU as this should keep the RAM to nearer the 1333 Mhz and might be a safer choice.

I have thought about that aswell. Dropping it to 1066 MHz instead. I havent OCd yet and i am not sure i will but I will keep all this in mind if I choose to. Thanks for all your research and help (applaud)!

[absic]

No problem and the issues concern me and the system I am running as well.

When/if you have a go at overclocking don't forget to let us know how you get on and post your results in the overclocking section of the forum. And, of course, if you encounter any hiccups feel free to contact me. 

[wanner]

No problem and the issues concern me and the system I am running as well.

When/if you have a go at overclocking don't forget to let us know how you get on and post your results in the overclocking section of the forum. And, of course, if you encounter any hiccups feel free to contact me. 

I sold my 945 today, and ordered a 955 BE instead. Now if/when i overclock i can just increase the multiplier .

[absic]

Good move but don't forget, the same rules will still apply even with an unlocked multiplier. It's just that, with the unlocked multiplier, it is much easier to increase the speed of the CPU without affecting the speed of the RAM.

[wanner]

Good move but don't forget, the same rules will still apply even with an unlocked multiplier. It's just that, with the unlocked multiplier, it is much easier to increase the speed of the CPU without affecting the speed of the RAM.

I thought so, felt kinda stupid since i bought the 945 just three weeks ago, lost some money became an experience richer .
My plan is to OC by increasing the multiplier. However I think its a shame I wont be able to run my memories@1600MHz as they are intended too.

[absic]

Yes, I feel exactly the same about that and in some ways I also feel that I have been cheated by AMD as they haven't made the situation very clear. Hence my research and this thread, as I think people should know the reality rather than the hype.

You may find that your new CPU will run OK with your RAM at 1600 Mhz and without issue, my 1090T does but I have actually pulled it back to 1333 Mhz especially after discovering that, in some cases, your system can appear to be OK only for the Memory Controllers to give up the ghost without warning.

And, to be totally honest, upping the speed of the CPU and keeping the RAM at 1333 Mhz will actually give you better overall performance.

[absic]

Here are a couple of AMD links that you might find useful:

Check here for Athlon ii CPU's: http://www.amd.com/us/products/desktop/processors/athlon-ii-x2/Pages/AMD-athlon-ii-x2-processor-model-numbers-feature-comparison.aspx

Check here for Phenom ii CPU's: http://www.amd.com/us/products/desktop/processors/phenom-ii/Pages/phenom-ii-model-number-comparison.aspx

You have to go down to near the bottom of the page to find the Memory Support specs.
From this info, when running a Phenom ii  the officially supported speeds are: 1066 Mhz if you are using DDR2 & 1333 Mhz with DDR3.
With an Athlon X2 CPU the official speed is 1066 Mhz with DDR2 or DDR3.
If you are running an Athlon X3 or X4  the official speeds are: 1066 Mhz DDR2 or 1333 Mhz DDR3.

Just to re-state my earlier comment, as I have had a couple of PM's about this, the official RAM speed limitation has been set by AMD and is not due to Gigabyte or the BIOS.

[absic]

Ok first off I must apologise for making a basic mistake when talking about Dual Channel/Single Channel and Ganged/Unganged Mode. In my attempts to make things easily understood I actually mixed my terminology and would like to clarify my error.

Gangedl 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 the majority of 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)

[IceColdBeer]

Thats great to know.

Especially since I've built 3 PC's using the Althon X2 processor.