Undervolting CPU to match lower TDP support of motherboard? \ VOGONS

Undervolting CPU to match lower TDP support of motherboard?

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First post, by data9791

Posted on 2019-10-28, 06:14

data9791 Offline

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Trying to build a powerful budget XP gaming machine at the moment. I've got a Phenom II X4 965 with a TDP of 125w, the only DDR3 motherboard I have that will socket this CPU is an Asrock 960GM-VGS3 FX but it's only rated for 95w TDP. The board will boot and work fine with the CPU, but I haven't put it under load. I know the 965 will undervolt very well all the way down to around 1.25 or so. Will it work to undervolt this CPU as much as possible and pair it with this board? This board has full XP 32bit support and came with 8GB of free RAM so it will save me quite a bit of money if I can use it.

Reply 1 of 4, by agent_x007

Posted on 2019-10-28, 07:57

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Yes, you can.
Going low enough on Vcore will make cooling it easier as well.

Reply 2 of 4, by shamino

Posted on 2019-10-28, 13:33

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CPU power consumption scales with the square of voltage, so based on that you can estimate how low it needs to be to get you to 95W. Based on the assumption that the original spec truly uses 125W, then you're trying to lower it to 76% of original.
if "x" is the new voltage, and "y" is the original voltage that AMD rated it at, then
(x^2 / y^2) = percentage of original power consumption
If you get that down to less than 76% then it's probably fine, but of course less is safer.

If you still feel like you're pushing it, then you could also look into improving the cooling of the MOSFETs near the CPU (flat 3-legged components) to help them out.

Reply 3 of 4, by bakemono

Posted on 2019-10-28, 14:08

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If the relevant BIOS setting exists, try changing the startup P-state to keep the watts down during the booting process. It should say P0,P1,P2,P3, or P4, and P0 is the fastest so any other setting would lower the speed/voltage.

Reply 4 of 4, by data9791

Posted on 2019-10-28, 17:42

data9791 Offline

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shamino wrote:
CPU power consumption scales with the square of voltage, so based on that you can estimate how low it needs to be to get you to […]
Show full quote
CPU power consumption scales with the square of voltage, so based on that you can estimate how low it needs to be to get you to 95W. Based on the assumption that the original spec truly uses 125W, then you're trying to lower it to 76% of original.
if "x" is the new voltage, and "y" is the original voltage that AMD rated it at, then
(x^2 / y^2) = percentage of original power consumption
If you get that down to less than 76% then it's probably fine, but of course less is safer.

If you still feel like you're pushing it, then you could also look into improving the cooling of the MOSFETs near the CPU (flat 3-legged components) to help them out.

1.25v using that formula comes out to around 80% of the stock vcore if I did the math correctly 🙁
I'll probably just run it that way, and buy pack of those mini heatsinks from China for a couple dollars and try to get a little little air flow over the mosfets. I'm going to be running 32bit XP with games from 2001-2009, so I don't think it will be all that stressed.

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