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Undervolting CPU or AMD Cool n Quiet

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August 7, 2010 4:53:03 AM

I have a HTPC that I leave on 24/7 so I want to minimize energy consumption. I am not interested in OCing the CPU (AMD X4 635) but want to make sure the system is efficient at the stock speed 2.9ghz. I was looking into undervolting to lower temps and power, but have heard Cool n Quiet already does this as part of its function automaticlly. So would undervolting the CPU not really make much difference. I have an ASUS M4A785M-T-CSM mobo and the bios settings are not that user friendly from what others on the net say. Would I benefit from Undercloking over using Cool n Quiet, or can I use both easily.

I also have another issue where I have Gskill DDR3 1600 ram (4gb) but the Asus board only reads 1333mhz by default - I know it can be overclocked to properly run the 1600 RAM and maybe even undervolt that as well, but again the layout of the Bios settings are not very user friendly - Asus forums have no info, and I have read posts that others are just as confused as me. I have read many articles and posts on the topic but when I go to my Bios, the choices are nothing like what others describe as setting.

Any help related to this particular mobo would be greatly appreciated.

Thanks,mh
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August 7, 2010 5:11:11 AM

You really only see a power consumption difference based on voltage when under load, so if the PC is sitting idle it's not going to use a lot of power anyway. I understand trying to lower it more, but yes what you read about Cool N Quiet is true, it already will drop voltage. If you can enable C States, in particular C6, it will even disable unused/idle cores completely - although to be honest I only know for certain that is an Intel feature so possibly not available to you. Anyway you can certainly undervolt on top of that, but make certain to check if it's still stable. If you're lucky you can undervolt a fair bit, if you're unlucky not at all.

About the RAM, 1333mhz is the default always. This is because it's the highest JEDEC spec (essentially the official guaranteed support). To reach 1600mhz you will need to OC the CPU, which means more voltage/power/heat. IMO, the best thing to do is lower your timings. If you have 1600mhz CL8 ram let's say, then you could probably get 1400mhz CL7, and 1333mhz CL6. By CL, it generally means the timings are 8-8-8-24, or 7-7-7-21 etc. At 1333mhz you might need, let's say, 7-6-6-19 or 6-7-6-19 or whatever. Just lower as much as you can, if it boots it's probably stable but a good way to check is either Prime95 blend tests or Memtest86+.

Oh, right, there's a caveat to that. Stock voltage on RAM is also like 1.3V or something for DDR3. Most RAM, however, is advertised at 1.65V settings which means if you leave the voltage at stock, you won't be able to attain rated speeds and timings. So in my example, 1600mhz CL8 RAM at 1.3V would only get something like CL9 or even CL10. I don't know exactly how much it's affected.

Since speed is really a none issue for an HTPC, IMO leave the RAM alone at 1333mhz and stock voltage just to save that little bit of power.
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August 7, 2010 5:35:51 AM

The RAM I have is 1600 CL9(Gskill ripjaws) - The mobo is reporting 1333mhz CL9, but the ASUS mobo says in the manual it can be overclocked to 1600 or 1800 ram. So you are saying I could only get the 1600 if I overclock the CPU as well.

I gues I kind of wasted my money on fancier RAM than I needed
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August 7, 2010 6:27:43 AM

Guitar1969 said:
The RAM I have is 1600 CL9(Gskill ripjaws) - The mobo is reporting 1333mhz CL9, but the ASUS mobo says in the manual it can be overclocked to 1600 or 1800 ram. So you are saying I could only get the 1600 if I overclock the CPU as well.

I gues I kind of wasted my money on fancier RAM than I needed

Not necessarily the case. There is a base clock, which I will say is 160 (Times the multiplier and you get your CPU speed), then there is a memory multiplier, stock its set to 8x, coming up with 1333mhz (8x160), if you up that memory multiplier to 10x, then your ram will run at 1600mhz.

(I'm speaking from an Intel standpoint though, so it may not be the same)
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August 7, 2010 6:46:42 AM

Actually, since that CPU can't use the full bandwidth of 1333mhz memory, you might as well just lower the timings a little at the lower speed to make latency lower.

Undervolting will save a few watts at idle, but if any load is put on the processor it will save many more watts. It also keeps the processor cooler+less stress from voltage being pumped through it, thus wearing it out less.
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August 7, 2010 6:52:19 AM

Quote:
Any help related to this particular mobo would be greatly appreciated.

Are you able to get a picture of the bios for us? I looked on google, but didn't find much.
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August 9, 2010 5:08:37 PM

Yea, there does not seem to be much about the ocerclocking capabilities on this mobo on the net. I have been unable to find any pics of the bios, and this weekend I tried changing the ram settings and crashed the system(Had to reset the cmos)

I got a few different responses, so I just wanted to clearify - would my best bet be just to leave the speed at 1333mhz (CPU is not goin g to be overclocked), and just set timing and undervoltage at that speed.

If so, I might try to get G.skill to help, as they will provide board specific settings if I ask, but I just want to make sure I ask them the right question.
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August 9, 2010 7:06:45 PM

Guitar1969 said:
Yea, there does not seem to be much about the ocerclocking capabilities on this mobo on the net. I have been unable to find any pics of the bios, and this weekend I tried changing the ram settings and crashed the system(Had to reset the cmos)

I got a few different responses, so I just wanted to clearify - would my best bet be just to leave the speed at 1333mhz (CPU is not goin g to be overclocked), and just set timing and undervoltage at that speed.

If so, I might try to get G.skill to help, as they will provide board specific settings if I ask, but I just want to make sure I ask them the right question.

You won't see any noticeable benefits of 1600mhz from 1333mhz bandwidth wise, so I would just lower timings and voltage as much as you can. If the ram is rated at 1.65v then you could leave it at that and use lower timings or you could undervolt them down to about 1.5v(no point in going lower to save power as every .2v is ~1W)and use higher timings.
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