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Core i3 and underclocking/undervolting - power usage


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I am planning a new home server/NAS and I have thought about Atom vs i3.


I have read various articles about low idle wattage of the i3 and wondered if it was possible to run the CPU at that speed constantly to minimise power usage.


I don't really need i3 performance right now, but I might in the future. What boards (if any in ITX) support underclocking/undervolting and what power consumption would I use by say dropping a core i3 530 2.93ghz to say 1.6ghz constantly?


How much "load" would I get if the system is simply serving files in NAS capacity to start off with?


Would it be favourable to a Atom? Presumably it would still perform a lot better.


Also - is there any difference in power usage of a H55 board in mATX or ITX format?


I have looked at the following boards so far in ITX:


DH57JG no underclocking? 4 SATA ports

Zotac H55-ITX underclock by 100mhz but only 0.10v drop (does that mean it can only go down by 0.1v or in steps of 0.1v?) but it has 6 SATA ports!

Gigabyte H55N-USB3 - supports underclocking but only 4 SATA? Only one PCI-E slot so futher SATA cards would negate a TV tuner


The purpose of my build is a home server with low power consumption and 2 x 2TB hard drives to start off with. I wish to add more hard drives and a PCI-E TV tuner in the future (waiting for new ones to support Freeview HD in the UK to come out).


So ideally I would like 5 or 6 SATA ports, and a free PCI-E port. The Zotac H55 is the only one I can see in that range - but I am not sure if it supports undervolting/underclocking.


The other options are mATX:


Gigabyte H55M-USB3 (and others). I don't need USB3 but I would like underclocking/undervolting - any other choices? What is the lowest power consuming board available?


Or Atom boards:

Gigabyte D510UD - 4 ports and no PCI-E

Zotac ITX - lots of ports, PCI-E but possibly broken (problems on the Zotac forums about using more than 3 ports = terrible performance)


I am also planning on building a HTPC to go with it with a i3 in the future/SSD/very small case.

Edited by tutu
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My personal opinion is i would not make any changes to clock speeds of the I3. While it is certainly possible to do what you are asking for, the gain will not be there. The power management of the I3 is extremely effective and you will only gain "possible instability" in trying to do that as you will alter the stepping function of the CPU. The idle down clocks are very effective right out of the box. It is very doubtful that we could represent a better "balance" than Intel has already done. Remember that the CPU goes into low power state when not being used so sitting there in a WHS it will not draw much power and of the power draw will be from what is attached. It is no secret (at least on this forum) that I a Gigabyte fan and have used the Micro ATX you listed and will be trying the ITX version soon. My guess (although do not have the power reading of the ITX) would be that at the wall there wouldn't be much difference as power comes from you drives, CPU, memory, as well as the board so I doubt you would see much of a difference. Depending of the efficiency of your PS, using two green drives I would expect about 45-55 watts out of the wall. the difference between an I3 and Atom in terms of computing power is staggering as I have both but minimal (10-15 swats savings) in terms of power consumption so my suggestion is to go the I3 and you will be ready for Vail when it is released.

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