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 Post subject: Which CPUs allow their voltages to be changed?
PostPosted: Sun Nov 27, 2016 5:36 am 
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I was planning on getting an i3 6100, then underclocking and undervolting it as part of my effort to make a super silent PC (I don't game so I don't care about losing speed). I was already investigating which PSU and CPU cooler to get when the concept of locked/unlocked CPU came to my attention. Try as I might, I can't seem to understand exactly which CPUs allow changing their voltage and/or frequency. I know that the k series are the unlocked and allow everything, but do locked CPUs at least allow you to change their temps? Maybe also underclocking but not overclocking (someone should tell Intel allowing this hybrid mode would be environmentally friendly, reduce electricity consumption, and wouldn't affect their sales which is the reason they locked CPUs to begin with)? I've actually read some exchanges in which they specifically discussed overclocking their i3 6100, several people in fact, so this all just keeps getting weirder and more confusing.


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 Post subject: Re: Which CPUs allow their voltages to be changed?
PostPosted: Sun Nov 27, 2016 8:54 am 
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Welcome to SPCR.

Don't have answers to all of your questions, but here's a couple thoughts. First, you don't need to underclock/undervolt an i3 to make it silent. Skylake does a great job of adjusting both the core voltage and frequency at will based on the processor load. Here's an overview. Practically speaking, if you are web browsing, the CPU freq and voltage will jump up during page loading and jump down after completion. Leading to your CPU mostly idling, consuming just a few watts.

So, if silence is the goal with a lightly used i3, all that's required is a decent cooler and some airflow through the case.

If, for the sake of experimentation, you do want to mess with undervolting and underclocking, it's mostly research to find a motherboard that has those options open. For undervolting, you'll want a board that allows a negative core offset voltage. Z170 boards are the most likely to have the option open - you really need to read through the manuals. Or hope someone will pipe up and and say their mobo has it.

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 Post subject: Re: Which CPUs allow their voltages to be changed?
PostPosted: Sun Nov 27, 2016 8:58 am 
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just_a_simple_man wrote:
but do locked CPUs at least allow you to change their temps?

With a 6100 you might do anything you want, providing the motherboard of choice let you to do that (allowing negative voltage offsets and multiplier manipulation).

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 Post subject: Re: Which CPUs allow their voltages to be changed?
PostPosted: Sun Nov 27, 2016 10:52 am 
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CA_Steve wrote:
you don't need to underclock/undervolt an i3 to make it silent.


My original idea was to go crazy and take it down to 0.65 volts and halve its frequency, which calculated from a stock voltage of presumably 1.20 volts would reduce watt consumption to barely 15% of normal values. I figured with this I might not even need a cooler fan, I'd just leave the stock heatsink+fan but remove the fan and the temps might just be ok. Incidentally, it would be nice if someone could do some test about this scenario.

By the way, maybe I'm mistaken but I'm reading a few comments that stock VCORE on the i3 6100 might be 1.30 or 1.35 volts. Isn't this a little too high? I would've expected something like 1.10 to 1.20.


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 Post subject: Re: Which CPUs allow their voltages to be changed?
PostPosted: Sun Nov 27, 2016 11:24 am 
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Not sure you'd have a stable CPU at 0.65V load, let alone idle. Stock idle is ~0.8V. Stock load voltage is a mess as most reviews are of the unlocked parts and Z170 motherboards. Which leads to a lot of the mobo mfgrs to screw around and use a higher than neccessary load voltage for "stock" so they can get bragging rights for better benchmarks in reviews..or another cynical reason is they want less customer calls about unstable overclocking. <shrugs> In any case, I think 1.2V is closer to a stock load voltage. Here's a fun chart from Anandtech's i7 review. Compare the mobo's "stock" settings vs the author's manual settings.

Not sure how far below 0.8V you can go in order to have a stable idling CPU at 800MHz. In general, dropping load voltage 0.1 to 0.15V from 1.2V may lead to a stable stock freq. YMMV. My wild ass guess is you might be able to drop load voltage to 1V if you half the clock multiplier. So, closer to 35% of stock load power.

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