Underclocking my CPU?

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i5Baby

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Hello!

I am currently working on a project to integrate a desktop into a small briefcase. I wanted to underclock my CPU to 35 watts so I could use a laptop cooler instead of using a fat desktop cooler. Or, I could use a 45 watt laptop cooler so I won't have to underclock it so much.

Many thanks!
 
Solution
emdea22
Laptop heatsink and fan should be definitely doable. The only way to know approximately how much the whole system draws is to hook up the psu to a watt meter (its about $5) and check. The main thing that uses power will be the PSU as efficiency varies.

So if the CPU draws 35W from the mobo -> the mobo power delivery is also not 100% so say that goes to 45W + ram + the mobo itself (SB+NB etc) + storage = say 70w (varies greatly depending on components). If the PSU has 80% efficiency then it will draw ~100W of power (given the efficiency is at peak at about 60-75% load)
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emdea22

emdea22

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Staying on topic - if the cpu has an unlocked multiplier then just check its power modes and monitor its voltage with something like hwmonitor. Then set the voltage and frequency to the appropriate levels. You can also enable a lot of power saving features through bios and windows.
 
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emdea22

emdea22

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i have the 5400k and i can tell you right now it would be easier if it were an intel BUT its still doable. These are the p-states of your 6400k
Low power P states [1] #1: 3600 MHz, 0.925V
#2: 3100 MHz, 0.775V
#3: 2600 MHz, 0.65V
#4: 2200 MHz, 0.45V
#5: 1800 MHz, 0.25V

I would suggest #4. Also since its an APU you might want to check the GPU side of things. If you leave the GPU on auto frequency it automatically downclocks and downvolts as necessary HOWEVER if you lower the GPU frequency manually then it will stay at that frequency all the time.
 
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emdea22

emdea22

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Laptop heatsink and fan should be definitely doable. The only way to know approximately how much the whole system draws is to hook up the psu to a watt meter (its about $5) and check. The main thing that uses power will be the PSU as efficiency varies.

So if the CPU draws 35W from the mobo -> the mobo power delivery is also not 100% so say that goes to 45W + ram + the mobo itself (SB+NB etc) + storage = say 70w (varies greatly depending on components). If the PSU has 80% efficiency then it will draw ~100W of power (given the efficiency is at peak at about 60-75% load)
 
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Solution
emdea22

emdea22

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An SSD or USB flash (only if using linux or windowsXP) are ways to cut down on the power draw. Also downclocking RAM to a lower frequency like 1066 and lowering voltage helps. There are many things you can do to get that whole machine close to laptop levels even if you'll probably not going to get as good of an efficiency as a laptop.
 
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i5Baby

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So, do I just look for an unlocked motherboard?

Oh, and here's what I am planning on using. Anything I should change or add/remove?

AMD A6 6400K Underclocked to 35 watts

4GB 1333MHz RAM (Didn't go with 1066 because I'm using integrated graphics, and that would make it real slow)

120GB SSD
 
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emdea22

emdea22

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You don't need an unlocked motherboard. All AMD motherboards should allow overclocking as well as underclocking. Things you should consider when buying the mobo are:

Adjustable voltages (especially on the cpu)
Small form factor -> mini-itx or micro atx
Cheap boards (like msi a55m-e33/p33) don't have adjustable voltage on the cpu so stay away
Preferably no wifi or Bluetooth on-board as those eat additional power
 
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