The FX journey into under-volting an 8 core CPU

I have had my FX-8320 for a little over a month, but I couldn't help but notice how hot in general these things run. Even though I am using the stock cooler, and the chip has never surpassed the 61c core temp danger zone, it has came close a few times. I couldn't for the life of me believe that the stock cooler for this chip was "that bad".

I just thought these chips ran a little on the hotside in general, and as long as you don't exceed 61c on the core and 70c on the socket temp, then everything was ok. That is true, but I had an idea to try a little experiment. I thought, lets see what the stock voltage is on these things, and see if we can lower that in any significant way and see what we get.

According to CPU World, the FX 8320 has the following Boosted Pstates (Voltage at Turbo Core Clocks)

#1: 4000 MHz, 1.425V
#2: 3700 MHz, 1.4125V

The Stock Voltage at 3.5 GHz is anywhere between 1.3375 to 1.3875v depending on the motherboard and manufacturer. On my Biostar TA 970 v5  the default Vcore was set at 1.3375 volts.

Now with this information in mind, I set out on my under-volting journey.

After digging around the BIOS, I found Custom Pstates under the Performance tab. I had to Disable CPB(Core Performance Boost Mode/Turbo Core) before I was able to adjust custom Pstates (Makes sense because we are changing the voltages). I tried a few settings dropping it down in increments. It just kept booting into Windows, and just kept being Prime95 Stable after an hour.

(This is what I used for this test so far due to time constraints, as I have found undervolts will usually either fail to boot Windows with a BSOD or it will fail Prime within 15 minutes if it doesn't have enough juice, where as an Overclock can go for hours before it fails prime.)

After some more tinkering  I found my FX 8320's undervolting limit. I was able to drop the CPU Vcore to 1.1875 volts. I tried 1.1750v, but the system would not boot into windows at that low of a voltage, so 1.1875 was the best i could do. The system was completely stable after 1 Prime 95 Blend test and 1 Prime 95 Small FTT test each ran for 1 hour.

CPU Core temp - never exceeded 45c on stock cooler with all 8 cores maxed to 100%

CPU Socket Temp - dropped 7 Degrees C and maxed out at 65 C (Socket Temp is safe up to 70c on this board according to documentation and BIOS Shutdown Temp is defaulted to 70c) and is located on the bottom of the motherboard under the CPU Socket...not to be confused with the Core Temp sensor located inside the CPU)

I am not even sure the Socket temps being read by HWMonitor are even accurate because its saying the these temps are that high on the socket, but EVERYTHING in the motherboard is cool to the touch while running (my laser thermometer is broke  .....) North Bridge heatsink is slightly chalking that up to HWmonitor/board glitch temp sensors....I can tell they are no where near 65 c You would feel heat somewhere on the board if something was 150F so im about 99% certain that is wrong. I base this on the fact the BIOS shows Socket Temps to be 10C warmer then Core Temps shown by Windows monitoring programs. As I have learned in the past, HWMonitor is not always perfect.

CPU-Z and Core Temp Windows

Overall, heat has been reduced significantly. Under full Prime95 load, my Antec Power Supply no longer expels tons of hot fact, My power supply fan didn't even need to spin up to full speeds anymore to handle the 100% load on the CPU now at these reduced voltages. Considering I went from 1.33V (1.4125 and 1.425v Turbo) down to 1.1875 volts, I expected as much. I was also able to drop the NorthBridge Voltage from the stock 1.200V to 1.1750 volts Saving even more power.

Going a bit farther, I used a KillaWatt to test power consumption before and after the undervolt at the wall plug, and the results were interesting!

Results Undervolted

Idle - 87 watts
Full Load 193 watts

Results at Stock volts and Bios settings

Idle 114 watts
Full load 238 watts

 Results from Top to Bottom: Idle Undervolted, Idle Full Load, Stock Idle, and Stock Full load.
Killawatt Undervolted Idle

Killawatt Stock Idle

Killawatt Stock Under Load

As you can see, undervolted, we were able to keep the total power draw under 200 watts at full load which is very impressive. At stock however, is a whole other ball game. At full load the system almost breaks the 240 watt number, and this is just at stock. Imagine if this sucker was overclocked....however, some serious speeds can be achieved when overclocking if you have the cooling to cope with it. The world record overclock is on an AMD CPU.

If you have an AMD FX series CPU, undervolting is a serious option, even more so perhaps then overclocking. Depending on the chip, it seems AMD threw a lot of voltages at these chips to ensure successful yields, which means you may have a lot of room to undervolt for energy savings instead of overclocking.

It looks like the FX chips are just as good undervolters as they are overclockers! I hope you had as much fun on this journey as i did! Till next time! :)

Disclaimer: I am not responsible for anything that may happen to your PC when changing settings or changing registry values. If you choose to make changes, you do so at your own risk.. You are solely responsible for any damage to your computer , data, or other hardware due to user error, inadequate cooling, too high of voltages, incorrect software settings, and any other factors. Please remember to back up your computer before attempting this. If overclocking, Do not Overclock on the stock AMD or Intel CPU Heatsink and fans. Use Aftermarket cooling heat sinks of sufficient TDP or water cooling to ensure best chance of not having premature hardware failure. As always, remember to backup your data before attempting any change. I am not responsible for data loss or damage of any kind. 

4 Responses to The FX journey into under-volting an 8 core CPU

  1. Worked for me. Chip was running way too hot before undervolting.

  2. thx a lot for this "guide", i helped a lot with my problems of throttle due hight temperatures on the MB

  3. Coming along years later as I'm looking to upgrade... but I ran an 8300 @ 1.1vcore, stock speed for over 4 years. It was stable up to 3.6ghz @ 1.1vcore. I tested it up to 4.2-4.4ghz range @ 1.25vcore right after I got it, but decided undervolting was best for me as well. Now I'm trying to see if I can't get it back up to the 4.3-4.5ghz range again to maybe survive until Zen 3 comes out, see if it's a new socket type, rather than upgrade now to zen2 only to find out they're changing socket next year and I bought into a dead end (exactly what I did when I upgraded from Core 2 to this FX).

    Anyway, point was, yes these chips handled undervolting very well.


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